These mansions are enormous, they're luxe, and they're definitely something that no one needs.
And by building big, we mean repeatedly typing 'motherlode' into the cheat bar just to get enough compensation. It's not likely that anyone on earth would ever turn down a mansion, so why should it be any different in the world of the Sims? There are some who opt for downsizing and can't be bothered with more than one bathroom and maybe a second bedroom, but then there are others who love to build big.