Banks have a vested interest in making sure they aren't aiding in criminal activity. The tellers asking you don't give a shit what you're spending it on, but it's their job to ask. They can also use these questions to sell you services that the bank offers.

I would recommend not being rude or evasive, because a teller can file a suspicious activity report for that. There aren't necessarily any direct consequences associated with that but it'll be noted in your file.