Are there not enough flights or quarantine is full? I don't see what possibly could stop a Thai from repatriating.
The Thai government is really thrashing with these requirements. Want to come 9 months? Get a STV, but only from low risk countries. Want to come for 1 month? Get a SETV, high risk countries no problem. METV I must assume has been suspended because it's basically the STV but with lower requirements. If your goal is controlling spread of a virus none of this makes any sense to me.