My reading is that in the suburbs you typically buy, while in urban environments you typically rent because all the land is already owned by someone who is making a killing off it; they aren't going to sell because that would be slaughtering the golden goose. And that prevents almost everyone who isn't a landowner from getting ahead, because as soon as you figure out a way to make a surplus, poof the rents go up and absorb it. Oh sure, individuals who perform better than average might be able to press their advantage; but class movement is impossible because it is always "priced in".

I am not sure that this phenomenon is unique to cities, in fact, but rather an inevitable endgame to the idea of owning land in perpetuity. It creates a permanent class divide.