TBF, in one episode they mention that grandpa Simpson sold his house to buy this one for Homer and his family with the expectation that he would then live with them. Of course they immediately shipped him off to an old folks home lol.

There's also lots of episodes where they have trouble paying bills and whatnot, so even with a fully paid off house they were still clearly struggling to stay alive water. In the latter years the show turned into "wacky adventure of the week featuring X guest star", but in the early years they did a decent job of humanizing them.