This is almost 100% due to developer churn. Every mid-level developer introduced to the project will think they have the new abstraction that will fix everythin

This is almost 100% due to developer churn. Every mid-level developer introduced to the project will think they have the new abstraction that will fix everything. Eventually you end up with a monstrosity partially implementing half a dozen different abstractions with no overall architecture. I've seen it many times. The fix for this is pretty easy though. Keep employees and avoid the churn.