[wl]

The big exception to this I've seen: The functioning bit of software was written in an oddball language that was already niche decades ago and the pool of developers who are competent to work on such a codebase is exceedingly small.

[jamesfinlayson]

Yep - I was at a company that replaced something super obscure - I suspect the number of people in Australia that knew the tech was like 10 to 20. The tech was so obscure I don't think there was any path out other than a full rewrite.

A company I worked at decided to rewrite a Fortran system - I suspect that if they wanted to avoid a rewrite they could have started breaking bits off into C and mixing the languages at the linking step... but I understand their desire for a clean break - a rewrite was going to take years but a migration would have taken even longer and been even harder due to the lack of Fortran developers.

[darth_avocado]

I would classify them in the “ existing languages/frameworks getting obsolete” bucket.