Is it only due to financial reasons or why do Thai girls like foreign men? There are several reasons why Thai girls see a foreigner as an attractive partner.
Thailand and Thai women
Beside its natural beauty, wonderful beaches, great cuisine, easy-going lifestyle, Thailand is also well known for it's beautiful girls, who in average are slimmer than Western girls - Sorry ladies, but it's the truth!
Many Western men are attracted to Thai women for several reasons. They look exotic, mostly tiny, slender body and look younger than they are. A 35 years old woman can look like a 22 years old girl. Compared to Western women, Thai girls have a more feminine and modest nature, they try to look as cute as possible (e.g. bunny ears, 'Hello Kitty' style). They are playful, slightly naive and childish in such a way that it arouses a feeling of affection and a protective instinct in men.
Western men like the 'Care-Factor'
Also, an important aspect is the so-called "care-factor". It is not unusual when a Thai girl will clean up her man's room on her own initiative. She will iron & fold his shirts, cook for him and do other things to make him feel more comfortable and to show him that she cares about him. This treatment is what some men miss in Western culture, where people in a relationship often compete against each other instead of completing each other.
Why are many Thai Women attracted to foreigner (especially Western) men?
An important point is "status": Men from developed countries enjoy a high social status in Thailand, regardless of their actual economic status. While a local factory worker would have little chances to date a girl with higher education such as a teacher, a Western man in the same position has indeed higher chances to win that girl's heart. There are several reasons for this phenomenon.
Level of Education vs. Language Skills
To Thai people, English is known as a world language and is part of what they call a good education. If you can speak english, you can speak to the world. A foreign man's English skills are often equal or better than those of local girls. This is in many cases a result of high education standards in many Western countries. Let's assume a random foreigner man has a lower education than a local girl. The fact that he can express himself better than her, makes him appear more literate, self-confident and superior, which compensates his inferior education. Thus, he still has good chances with this girl.
Impact of Western culture
Throughout the last century, Western culture has had a great impact on the world, through innovation (e.g. IPhone, Internet), movies, music and trends. Most noticable, popular and well-known politicians, scientists, moviestars and popstars (such as Justin Bieber) originate from the Western world. This inevitably has had an impact on many Thai people's way of thinking and lead to a higher regard towards Western people in Thai society.
Language & Cultural Barrier
Another point is the language (and cultural) barrier. A person’s bad sense of humor, weirdness, nerdy nature, goofy behavior and other negative characteristics are less likely noticed by the other person, when talking in a foreign language.
For instance, an American girl would soon quit a conversation with an American guy that makes terrible jokes (she’d consider him as a moron and thus a loser). In contrast, it would be different with a Thai girl. She would be more tolerant and give him more chances, because either, she wouldn’t understand that it’s a terrible joke (language barrier), or she would assume that in the Western man’s culture, it’s actually not a terrible joke (cultural barrier).
Thai girls who don't like Thai men
Some Thai girls keep saying to Western men they are not interested in Thai men at all. These women claim that Thai guys are not their type or that they have a bad attitude. While in some cases it might be the truth, there is also often another side of the coin. After all, one should raise questions why a girl doesn't want a fellow countryman who shares the same language and culture.
Often, these mentioned girls have been avoided or even looked down upon by Thai men. The reason might be this very girl's bad attitute itself. Her behaviour, educational background, her values, her looks or the way she talks might not be conform with those of an ideal, polite and decent girl favored by Thai men. Local men can quickly see this and label her as low class girl, whereas foreigners can't tell due to language and cultural barriers.
In brief, by telling Western guys about their lack of interest towards local men, some girls deny the painful truth that it's actually themselves who have been avoided by these men. It's a psychological defense mechanism to distract from one's own flaws. While some of these girls really prefer Western men, others engage with Western men as a "backup plan", a "second choice" as they can't get (local) alternatives.
Looks & Appearance
Also, another reason for foreigner men’s high status is their appearance and looks. In Thai society, white skin color is associated with beauty, pureness and wealth. Thus, Western men with bright skin appear more attractive. Of course, features like a beard, tallness, ‘Western’ nose and eyes also play a role: Large, colored eyes, large nose and a dense beard are considered as attractive aswell.
Thais often don’t understand why a handsome foreigner man sticks with a tan skinned, north-eastern girl (regarded as lower class), while he could also have a pale skinned Thai-Chinese counterpart that is favoured by most Thai men.
Perception of Beauty & Competition
Many Western men are dating a (in their own view) gorgeous Thai girl, while in their own country it’d be harder to have such a ‘catch’. Again, this might be due to a different perception of beauty in different cultures. Local men might consider her as less pretty and are less interested in her. Consequently, a foreigner guy has less competitors, which makes the whole dating game more lucrative for him. After all it is the same principle all around the world: Demand determines supply.
The Economic Factor
Of course, the economic factor also plays a significant role. There are clichés about many locals girls chosing their foreign partner due to his better economic status. They are not completely false. Indeed, there are a few girls who don't consider their partner as attractive and stick with him only because he is supporting her financially. However, in most cases, the foreigner man's (higher) financial status is not important to the local girl. Or, it is only one of his features (among many other aspects about him) that make her feel attracted to him.
Foreigners, who can afford to come to Thailand mostly earn more than the average income in Thailand. Even if the girl doesn’t directly benefit from his economic status, it will make him appear more attractive because he seems to be independent or possibly earns more than her. Potentially, he seems to be able to provide for her and her future offspring. However, this seems to be related to evolution (women seek men who can provide) and can be observed throughout the world - not only in Thailand.
When walking on the streets in Thailand, you will encounter many mixed couples and, in 95% of the cases the guy is a foreigner and the girl is Thai. This is because western women are attracted to taller men, that have equal or higher economic, educational and social status. Vice versa, Thai men prefer slim, smaller, more modest and more feminine girls compared to Western women.
And those Thai men who even attract Western women are “Alpha” males and usually can choose from a larger list of prettier and younger local girls. Thus, she won't most likely be the 'chosen one'.
Consequently, it's relatively rare that a Thai guy is dating a Western girl.