> It maybe tech debt depending on a lot of context, with old tech you get into a lot of situations like this:

Yeah absolutely that's a fair example of tech debt, where a tech stack is so old that it's difficult to impossible to support modern features. But "classic ASP doesn't support this modern feature requested by product" is a lot different than "I don't like working with classic ASP."

> Formerly popular is also a red flag, over time it will get harder to hire.

Really depends. Java is a great example. Very unsexy, not too many startups beginning life as a Java shop, most code is likely "legacy" by this point. But Java is so ubiquitous, if I were a Java shop I wouldn't be worried whatsoever about running out of Java expertise anytime soon. Maybe in 50 years.

On the other hand, if you were a legacy Java shop that jumped on the Scala hype train at its peak 8-10 years ago, or God forbid you built something in Haskell when it was getting touted as the next big thing, you're in a far more precarious situation. Ironically, many Java shops tried out Scala as a way to move their Java codebases forward, and now their now-legacy Scala 2.xx codebase is a way larger technical dumpster fire than their Java codebase.