Except the average US mortgage holder buys and sells a house every 7 years. For the first 7 years the amortization schedule means you're paying almost all interest and building very little equity. You're also paying realtor fees and transaction costs each time.

So while paying off a 30 year mortgage might have been to pay off the house and keep it forever, that's not how Americans treat it. They basically use it as a way to get 10-20x leverage on housing prices speculation, and if they profit, cash out 7 years later and do it again with a new house.