I worked on one such app. It was lost in the cross fire, I was asked to try to fix a bug. I came back and said this wasn't a bug, it was a badly built system. If they wanted me to work on it, I'd need a few sprints dedicated to it. They passed. A month or two later, it was impacting some crucial flows. We revisited it and funded it. I AB tested the rewrite against the original and saw a statistically significant improvement in user behavior. We retired the original, I presented my findings to our product team. They agreed it was impactful.