That's wild. In the US, a fixed-rate 30 year is pretty common, particularly when rates were <4% - lock in that low rate for the duration. We currently have a 20 year. No prepayment penalty, no renegotiation. The only reason my monthly payment changes is changes to taxes/insurance (paid with mortgage, put into escrow to ensure those are kept current). I effectively have a housing cost that goes down over time due to inflation and salary increases.

I suspect a rates go up, ARMs (adjustable rate mortgage) become more common, in the hopes that rates come down and the homeowner see that upside.