I socked away and invested everything I could during my career in Silicon Valley. I retired just a few months after my fortieth birthday.
Why most of my colleagues didn't do the same and instead 'leveled up' their lifestyle to match their income is beyond my capacity to understand.
There is also the problem that many bought real estate far before it was as fiendishly expensive as it is now, bought stocks and were part of companies during wild bull runs, and act like you can reproduce their success trivially. (You can’t)
Also, I think of spending in your youth as an investment in memories. What is the point of getting all your best trips in at 65 (just before dementia sets in) when you have at best 30 years to enjoy them. If you did the trips when you’re 30, you’d have decades more to enjoy them and could actually go on them. Living for when you’re senile is a scam.
Everything's more fun when it's new and you're learning fast, but less and less seems new as you gain experience. A lot of "new" things are obviously reincarnations of things you learned long ago. Others just seem obviously stupid according to whatever biases you've accumulated (and we all do). Over time, you have to roam further and further afield to find anything truly new and not stupid. Sometimes that's so far afield that it's beyond anything that would have ever interested you even when young.
As for teams, well, some things are just pretty constant. What job is not going to have tedious planning sessions, testing woes, source-control and deployment drudgery? Only one where you're a prima donna pushing all of that onto other people, or one headed for disaster because you're all incompetent cowboys. If it was all fun and games, they wouldn't pay so much for people to do it, and liking your immediate team only gets you so far.
Neither burnout nor retirement is like a light switch, going instantly from love to hate of the entire profession. It's a gradual weakening of the attractions and strengthening of the discontents, until you reach a tipping point. It might seem sudden or unexpected, but quite often it really isn't. It's something people can plan for, and that many more should.
As for what to do after, why do you assume that not wanting this career any more means not wanting any career (or hobby) at all? Second careers are not uncommon, and often one of the things that's frustrating about "always on" tech work is being pulled away from something else one enjoys. "Software development or nothing" seems like a really bizarre dichotomy.
Knuth has a wonderful take on how he is spending his retirement that I find inspiring: https://www-cs-faculty.stanford.edu/~knuth/email.html
...my role is to be on the bottom of things. What I do takes long hours of studying and uninterruptible concentration. I try to learn certain areas of computer science exhaustively; then I try to digest that knowledge into a form that is accessible to people who don't have time for such study.
Do you publish your digested knowledge anywhere? Do you have a blog?