>jeopardises the hard-won knowledge from years of working on and working with the software We have issue trackers and robust source control these days, that's

>jeopardises the hard-won knowledge from years of working on and working with the software We have issue trackers and robust source control these days, that's not really true unless someone wrote poor commit messages and didn't write anything on the issue. You can roll that into the new specs if you take the time to document. Knowledge preserved. The only hard-won knowledge you should be fighting for is business knowledge, which can be dependent on your UI/UX decisions. If you rewrite and change that substantially, yes, you lose that knowledge because you've obviously changed the UI/UX. You now force all of your users to relearn your product. Plus, you're going to get a whole new category of bugs with that new UI/UX. All of this was made more difficult back then by not having the modern language features in stuff like Rust and .NET and Go and Python that's made stuff easier and safer. Rewriting .NET -> .NET is much, much easier than C -> C. If you change languages, that's worse, and you'd have to completely learn two languages and all of their painful/weird points AND translate between those two (if you thought JavaScript equality was bad...)