Yeah that is what it boils down to often; the user doesn't care. It's more about what's best for the developer.
The problem is that a lot of developers want to work with what is 'sexy' at the moment. That's one factor that also drives e.g. job adverts; most vacancies I've seen will have "cryptocurrency" and "IoT" sprinkled in, just for the sake of looking attractive.
And old applications get rewritten in newer tech because of a combination of technical debt and developers going "I did not write this so I cannot read it and do not want to work with it".
Granted, newer programming languages (or versions thereof) often have better developer ergonomics (I spent my morning trying to get a C codebase to work while with my new Go codebase it should be a matter of installing the Go tools and doing 'go build').
Another factor is the perception of productivity; rebuilding software greenfield will feel super productive for at least the first six months to a year, after which things become more of a slog as the backlog fills with bug reports and change requests, instead of new features.
Source: I've seen this happen a number of times.
Disclaimer: I'm in a rebuild project myself now, the old codebase is nearly 200K of very poorly written PHP / JS, and the Decision was made to rewrite it from scratch. I'm going with Go and React at the moment; Go because it's unsurprising and boring code that should be fine for the next decade, and React because it's a de facto standard now and should be fine for the next 3-5 years as well. Both tools were decided on in part for future developers that will work alongside or to replace me.
But I'm sure in a few years my opinion on what is the best tech stack may change, idk.