> Some web searching suggests that only about 2% of home mortgages have prepayment penalty clauses.

It's clear (to me) that you're talking about the US specifically, but it might not be clear to everyone.

Residential mortgages are highly idiosyncratic to the country you're talking about. Try getting a 30 year fixed rate mortgage in the UK.

is there somewhere where a majority or a plurality of mortgages come with a prepayment penalty?