Banks make money on interest. Perhaps the principle itself is the issue, if it's legal to earn money on loans, no surprise a bank incentive is to make you take loan, and have you keep them for as long as it can.

Typically a mortgage does not allow over repayments. Why? It would get people in the nasty habit (from the perspective of the bank) to pay back a little more every month with the spare they've got.

Of course you can pay a fee to overpay.

What country is this?

I believe this to be illegal in the USA but would not be shocked if a rule change was slipped into some random unrelated bill.

If we're talking normal credit cards in the US, you technically are getting a 30 day loan for free, no interest if paid in full every month.

I don't see a issue if credit cards charged 30d interest on balance, but if mine did that I would drop it instantly.