It seems to me that this need to have too many things might be why Elly does all those loads of clothes every single day; we get broad hints that it's because Mike cannot put them away properly or put them in the hamper without mixing clean clothes in with the dirty thereby making what looks like a case of OCD actually a case of inconsiderate spoiled jerk of a child.
The problem with that reasoning is that it's not as simple as Elly would make it. Leaving aside the very obvious problem of his having outgrown certain garments that his mother simply cannot bring herself to dispose of, we have to remember that the huge pile more than likely contains clothing that is out of season and gifts from well-meaning outsiders.
This excess leads to problems because Elly seems to have not considered that Mike's fumbly little eight-year old hands simply cannot put clothes away the way she wants. Not only does he not have enough space in his dressers, he cannot reach the coat rod in his closet nor can he work a hanger effectively. This means that treating the floor like a large, low-hanging shelf is pretty much a necessity because his mother can't seem to figure out how to help him be neat.
What really makes him screwed is that Elly is averse to advice because she thinks that picky-faces are trying to humiliate her. Since she won't accept help and needs to feel persecuted, Mike never will learn to look after himself and have to rely on a wife to keep his environment in order.