Some of that is for shooting. Like on The Fresh Prince Of Bel-Air, Uncle Phil can definitely afford a house that big, but its layout is bizarre. The downstairs is dominated by a living room and kitchen in a sort of L shape that does not match any exterior shot and is a frankly mediocre use of space. It's because there's three cameras roving around where half the walls should be. And a live studio audience! They have to see and hear what's going on, or else it might as well be a laugh track.

Basically - it's a stage. It's not a set. You're watching a briskly-edited play, with an unusually high sense of verisimilitude. So yes, if you map out Jerry Seinfeld's apartment, it's deep and spacious and maybe doesn't connect to the hallway right. But that's just to give the actors somewhere to move. On-camera, it looks compressed, with very little of that floor space visible, and the back office simply left as a hand-wave for whatever you think is missing.