A good developer can totally put away a net surplus year to year while living normally. Personally I've always found it far more enjoyable to be good at what you do, cherry pick jobs and take "mini-retirements" between them than sock away cash with the goal of never working again. To each his own, I suppose.
I retired in my mid-thirties and almost everyone I told before hand had the same or similar pejorative response as yours... "Oh I could never do that" or "I would be bored" or even "Why would you want to do that?". I ended up stopping to tell people.
There is so much you can do when you've disconnected your employment from your living expenses. Not _having_ to work is very different than simply not working. You can work on what ever you would like. You can ask to work 2 days a week for 20% pay. You can work on mastering something completely different like woodworking, cooking, and instrument, or even something around software development. But to just associating FIRE with a monk-like or sedentary lifestyle is an overly broad and often inaccurate representation of the community.
What have you been doing in retirement?
Now I just do most of the same things, but with a more relaxed pace and with time in between to transition. For instance, if I meet a friend for coffee on a weekday morning I used to have the pressure to rush off to work afterwards. Instead, I can stay at the coffee shop afterwards and enjoy a quiet moment or read a book for a few minutes before moving on to the next thing.
Technology related... I moved from software development to doing building small electronics, learning to soldier components, and 3D printing cases. Currently I'm building a small device out of wood that has a round matrix of LEDs embedded that lights up and tracks satellites as they pass over my house. I have no idea what I'm doing really, but its been fun.
You are thinking about the right problem though–when I was in my twenties I mostly focusing on want to not work, rather than what I was going to do once I wasn't working. It's important to understand what your true goal is so that you can make sure FIRE satisfies it or you can set yourself up for some post-retirement blues.
In other words, some 40 year olds are indistinguishable from 30 year olds. Others have all sorts of minor chronic issues that pile up and lead to a miserable second half of life. Health and disease are "nonlinear" -- a health problem often snowballs into others.
Sleep seems to be a big one. Most people sleep poorly and don't know why. This leads to problems all the way up the chain, like heart issues and dental problems.
Diet is obviously another foundational issue. It's hard to eat well in many parts of America if you don't cook. Ordering from a restaurant every day is a way to eat too much salt, sugar, and fat. And yes I realize that lots of people are rolling their eyes at that.
It sounds like a minor issue until you compound it over 20 years. In other words, it's something you don't really care about in your 20's and 30's. But it catches up, and I recall reading a thread about "being old" on HN where lots of people mainly regret and are scared of health issues.
Exercise takes time too. I exercised 5+ days a week when working, but now I do it even more, and it's worth it.
You can obviously pay attention to your health and work at the same time, but I find that many people don't (e.g. in San Francisco).
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edit, found the thread: https://news.ycombinator.com/item?id=24527978
Practically speaking, it would be very difficult to find this kind of work situation in tech.
It probably doesn't really work for a more generic mid-level developer sort of situation where there are daily standups etc. (Or really any job that requires a lot of day-to-day communication and work.)
I could imagine a small startup getting quite a bit of value from getting a great FAANG-type engineer with 15+ years of experience for 50k /year.
I think that the real difference is that our city has actual lack of developers, so the developers that exists can demand things.
Having expensive medical bills puts a kink in many people's FIRE plans. For LeanFIRE atm it isn't an issue because the ACA will pay all or most of their health insurance in many states.
One can surely take mini-retirements between jobs, but realistically, it's harder to get salary bumps when you NEED a job and you don't have the luxury of choosing to stay at your current spot if an offer isn't an increase. Also one normally needs to stay at jobs for two years or otherwise can look like a risky hire.
Five years of semi-monastic living with a good dev salary can be enough to buy freedom to work as little or as much as one chooses for the rest of life.
The closest I've seen would be Early Retirement Extreme. He's still not exactly about deprivation, but rather self-sufficiency. And he targets lower income levels than a competent software developer.
Most blogs I've read have focused on enjoying your life without being wasteful with your dollars. It's easy to spend money that doesn't return nearly what you might guess or hope when you click that buy button. Just a small effort can change your thought process and better optimize your use of money and improve your lifestyle.
While many don't despise their career, everyone prefers having complete say over how they spend their time to having to do what a boss demands. If you still prefer working, that's great, but if you don't have a choice about it, you're likely less happy about that.
An alternative might be to build up a nest egg, and use free time outside of work to experiment with education, hobbies, and other activities, and find out if any of those give you enough of a compass towards creating and achieving that you need the employer less and less for the structure it hands you.
I've never had a particular desire to retire especially early.