[throwaway2k04]

One of the major mistakes that are made in re-writes is that the developers writing the new code are not always the ones who created the original code. They see complexity, but don't know if it is accidental complexity ("tech debt"), or necessary complexity.

One example from my own experience was a team that inherited a service that had already seen a major rewrite/refactoring to be prepared for requirements that the old team knew with certainty was coming. The new team created a new service that barely covered the needs that the company had at the time, and claimed that the new architecture was flexible to cover any future need (without actually investigating the needs that were already known). When they were tasked with supporting the new requirements, the end result was more complicated and less capable than the old service.