As an old dev (47) who's main focus is now management (the only thing I still program is devops stuff), there are some reasons why I stopped being a developer a few years back:
1) Developers are treated without much respect. Seriously, even with the scarcity, and even when we do get paid well (which is relatively rare) and have nice perks, developers still don't get the kind of respect other similarly highly skilled professionals get. At some point, when you get in your mid-30's and compare yourself with other professionals in the same age group, this really starts to grate.
2) The vast majority of companies still doesn't know how to make developers function properly. Those of us who discuss stuff like Agile, "manager / maker schedule", remote working, the pros and cons of open office plans, etcetera form a tiny minority, and we live in an echo chamber. 90% of all devs are still code monkeys in the basement. As a developer with a bit of experience and authority I decided to put my effort in changing that (i.e., get into management) to make life better for other developers.
3) I felt I was just repeating myself, basically doing the same thing on different platforms in different languages. I found it harder to learn new stuff not because I got "too old to learn", but because I didn't see anything particularly "new" in it, just same shit, different platform, which wasn't particularly motivating. (The only exception is the "cloud", because approaching the infrastructure as a dynamic, programmable resource is actually something new and challenging.)
Salary is still very much an issue. All this talk about developers getting paid so much is total bullshit, with the possible exception of a small minority of SV companies. Developers are seriously underpaid compared to their economic value and scarcity, and it's mostly just a matter of a lack of respect for "techies".
Personally, I don't care about the money (as a manager I currently choose to not get paid more than my best developers, which is making my bosses kinda nervous), but the feeling of getting screwed just pisses me off.
Most of you that are reading this: you are most likely not getting paid what you are worth. Not even close. Yes, even those who think they're doing fine. I've seen the numbers, and as a profession we are collectively getting screwed, with very few exceptions.
There are many professions in which people are less scarce, require less skill, knowledge and experience and add less economic value and still get paid considerably more simply because they are not "techies".