One of the reasons: at that scale the cost of identifying and refactoring reusable code into shared modules just isn't worth it. Your project may have somethin

One of the reasons: at that scale the cost of identifying and refactoring reusable code into shared modules just isn't worth it. Your project may have something in common with my project, but I wouldn't want to refactor my code into something that your project can use because I don't want to maintain that dependency. I expect the reverse to be true, so you often copy code and build very purpose-driven code for your project. It's not like anyone could be well versed in more than a tiny percentage of the entire codebase, so the gains from that kind of reuse just aren't there.