There are reasons why the U.S. and UK don't hand out extended visas for Thais easily, i.e. possible illegal work. (That's why, for example, as a female Thai tourist under 70, you can expect to be interviewed by immigration every single time you enter Hong Kong, even for short visits.)
As for foreign tourists, have you ever seen Yanks and Brits working illegally in Thailand as dishwashers or masseuses?