they don't just close it. They freeze it and you have to go in and show your visa and identity to unfreeze it. If you no longer qualify then they close it.
your inability to open an account has nothing to do with the Thai government. Those are bank decisions to limit their liability. There's no law or regulation telling the banks they can't open an account for you.
LTR is the best visa available if you qualify for it. Its cheaper than the other options long-term and offers much better benefits, including tax free status on foreign income.