Why does the bank take a service fee out and then put it right back the same day like oops?

Afaik they do that with Student bank accounts a lot. They'll base the student account off one of their other accounts. At CIBC in Canada they base it off an account with scaling prices for transactions, up to 14.95 for unlimited transactions, and then at the end of the month, charge the price and then refund it.

I'm not positive but I'm pretty sure that it's so they can charge you a fee for running into the negatives since bank fees don't actually need money in the account to be applied (unlike purchases).