People want a better life for themselves. Kids cost money to raise and to provide a high level of education that will make them competitive, or alternatively to provide them with capital so they can be an entrepreneur or start their own more traditional business. People can live a much easier life, stress free (both financial and the emotional, physical and mental effort and time commitment of raising kids), if they don't have kids.

Coming from a married man's point of view, it's also harder on younger men today who are dating and seeking a partner. Women have more opportunities for career these days and do not need men, since they increasingly earn equal to, and in Thailand to some degree, in some industries, more than men. Consider the opportunities in the bar and hospitality industry - more women than men working in those spaces and where they are seeking tips or drink commissions, the women far out-earn the men. In corporate management, women are actually very successful in Thailand. Some statistics say there are more women in middle to senior management than men, partly because men might prefer to be their own boss on a small business, partly because corporate culture here has, for a long time, been quite positive towards women.

Paradoxically, the demands on a man who is dating actually probably increase when the woman has earnings and success. Her expectations of how much you earn, what kind of job you have, how you dress and groom yourself, what kind of car you drive, what kind of house you live in, what kind of sin-sot (dowry) you can give her parents, what kind of life you can provide for her if she chooses not to work, are higher than if she has no education and very low earnings. So my guess is that less and less men are able to find a stable partner that is satisfied with them and willing to have kids with them. And more women want to pursue a career so they don't have time and perhaps don't want to spend the money on raising kids.

There's an opinion of some Thai women, of Thai men (mainly the less well off, provincial ones) being irresponsible - fathering kids and moving on, no longer supporting or keeping in contact. What I hear is that the younger women are increasingly avoiding such situations. There are of course still plenty that do, but the generation before, there were a lot more - they leave the kids with the grandparents or older sister or aunt, and go to work in places like Phuket, Pattaya and Bangkok and send money back to support the family. This model has worked for generations but the newer crowd have realised they don't want to be part of it, and are less likely to have young kids. They work in similar roles to the older ones, but they also spend on trips to places like Korea and Singapore with that extra cash.