Because people are too stupid for their own good. They are getting scammed in droves and cry endlessly when they fall for it. So now the government is trying to protect them from themselves.
You're going to have to have 25k in your Thai bank account getting almost no interest too if you want to get an extension in Thailand. So yes, it has to be in a bank account. What that requires and what you miss out on is on you. Thailand doesn't care.
if you want to do it yourself then you have to do it the official way. Which means leaving Thailand and applying online for a Thai visa. They DO NOT require a Thai bank account. They just require a bank statement from your bank anywhere
that's not what many people have experienced and posted about already. But each branch manager can basically do whatever they want. Which is why the policy makes no sense to begin with. Because many bank branch managers are still accepting agency money to give the letters without freezing anything
your understanding is wrong. Immigration in Thailand doesn't accept foreign bank accounts for anything. Only embassies accept those. Everything at immigration is Thai bank account. You'll have to leave Thailand and apply for the non-O at an embassy.