The Case Against 30-Year Mortgages

This isn't about 30-year mortgages in the general case, this is about the US specifically, where a fixed-rate 30-year mortgage is typical, with a good rate and no early repayment penalty.

And yes it's insane, because if rates go up you leave it alone and if rates go down you remortgage at a lower rate.

that's how all bonds/loans work

It's not how bonds work because you can't pay off a bond early other than by buying it on the open market at the prevailing price.

And furthermore, not all loans are fixed-rate. UK mortgage rates are relative to the Bank of England base rate.