> Does that mean each generation has to practically rebuild the houses of its parents?

Yes. In part its disposable consumerism but also its likely that something built in a period of rapid change (as suburbanism often builds houses on fields) may also be required to change itself after some time. In my area its common to see inter-war single-storey cottages rebuilt anew (knocked down completely with a new structure built from scratch), subdivided into two lots or amalgamated with others to build a block of apartments.

> Don't several story buildings pay for themselves

I mean dead-flat as in no steps in the ground floor within your building. Not as in 'single storey'.