I think people are confused by the term (length of fixed rate) versus amortization (total time to pay off debt).
In Canada mortgages are typically 25 or 30 year amortization periods, but you can only fix the rate for 10 years (usually less as you get a much lower rate).
After the 5 years you renew your mortgage at the current interest rate with the same bank, or try and refinance entirely which requires the same paperwork as a new mortgage.
The US and I believe Netherlands are the rare countries where you can get fixed rate for the entire 30 year amortization period.
Of course people tend to pay mortgage early to avoid paying many times over at 10%.
But, having small montly payment helps in case you have some temporary financial emergency.