It's kind of like conventional depreciating capital assets like buildings. A building requires maintenance, utilities, taxes, repairs and so on. If your building is too large for your needs, the costs can become a debilitating albatross round the neck of the business. There have been plenty of European aristocracy bankrupted by having a house that was too big.

In programming terms, it's very tempting to say, "this room is untidy, I'm going to build a new one." It's certainly more fun than tidying your room. But this is how you get sprawl and bloat.