[bubblyworld]

I think a source of bitrot the author doesn't mention comes from a combination of two things:

1. People modifying a large codebase generally don't have a complete understanding of the codebase (and this becomes more common the larger the codebase is). 2. "Chesterton's fence", i.e. modifying something you don't understand often has downstream effects you are unaware of.

It's the codebase equivalent of the 2nd law of thermodynamics - entropy always increases =).