People used them because they worked better than alternatives, not because they were p2p. Indeed, most people used them like centralized services by going to The Big Site We All Know and downloading things from there. That they weren't actually downloading the movie/game/etc from there was an ignorable implementation detail.

Young people today use centralized streaming sites more, because they're easier to use. That they're not p2p isn't something any of them know or care about.