They can't afford it, they have had problems with people not showing up, they know that they don't pay enough to attract people anyway.

The visa rules changed in October of last years. A huge percentage of Thai ESL teachers don't have work permits. Every month they would go to the nearest border, cross, and come back in with a new 30 day stamp in their passport. there are people who did this for seven years or more. Now you are allowed only 90 days using the entry stamp in a 180 day period, then you have to leave for a country with a Thai consulate and get a tourist visa.

It has all been really unclear, inconsistently enforced, and rather fluid. And if they don't want to, even with a visa, they don't have to let you in. So some people are just getting fed up, and leaving. And some who might have stayed under the old method don't want to bother now.