I spent 3.5 months there last summer. Having a bank account made it much easier to transfer money, gave me access to "scan to pay" and Bangkok Bank has cardless withdrawals so I didn't have to carry my debit card.
There's also the fact that I already had a bank account that was working fine.
If you want to accuse me of money laundering, there are the Thai defamation laws. Do you want to run into that kind of criminal trouble?
Also, there are countries where I can easily open a bank account, I know someone who has an account in Mexico. It's really handy for taking advantages of exchange rate variations.