Also I feel what usually happens is that requirements change over time, and things get repurposed as "hacks" because ain't nobody got time to rewrite the entire thing.

But at some point the effort to rewrite is worth it and at that point even the same engineers who did the original implementation should be able to write a much cleaner and faster version.

When I was new I thought I was so awesome when I saw how I could write better code than I read. It was only way later I realized people usually had good reasons for writing it that way originally but those reasons disappeared.