No, that isn't how it works. A DTA doesn't make you tac exempt. You still have reporting requirements in 2 places and will need to fill tax returns in Thailand. This means translating documents, hiring an accountant, submitting tax forms every year to RD.
Have you read your specific DTAs? Many of them just specify who has first rights to tax, not exclusive taxation rights. In many DTAs you will pay tax in both countries and rhe country with first rights on tax will provide a credit you can apply to the second country to prevent being taxed on the same income twice. If the rates in the second country are different, you pay the difference. Thaikand has much lower income bands than a lot of other countries, so many people will pay twice in both areas. It all depends on the DTAs but regardless, everyone will have a burden of dealing with more paperwork and beauracracy
Also a lot of people have income that isn't covered by a DTA