Thailand is deliberately making things difficult for themselves when it comes to hiring teachers. Sure, more money would be nice but the ability of the teachers wouldn't change much. The same people may stick around for longer or may move to more remote locations....but money isn't the answer.
The Thai government could make it a whole lot easier for native English speakers to want to be here with a few simple changes that would cost nothing.
1 - Scrap the insane paperwork and the expensive need for 'visa runs'.
2 - Reward long-term English teachers by doing the following: After 10 years of full-time teaching service award residency cards. After 20 years of full-time service, award citizenship.
Make it possible for educators to have a decent life in Thailand and good teachers WILL COME!