Banks banned Credit Card purchases for Crypto because they are missing out on a CASH ADVANCE FEE plus the HIGHER APR ON CASH ADVANCE FEES.
I know this because I am a banker at a USA bank.
Yes there are a lot of other reasons (some probably more important that the fees the banks are missing out on) that banks will not let you use "Credit" to buy Cryptocurrency.
The thing is, banks (yes not all of them) will allow you to use the money you worked for anyway you want to. It is very limited to what you cannot get with using our bank debit card
Credit=Money the banks trust you with but its not physically there
Hard earned dollars=the money you deposited into the account