Hobbies require money, but a lot of hobbies don't require very much of it.
Yeah, if your primary hobbies are skiing and golfing and traveling and rebuilding 60s cars, that's not going to come cheap. But there is no shortage of much cheaper hobbies.
Then they get to retirement and realize that doing the amazing things like traveling the world requires a lot of money.
Partition living expenses from hobby expenses, and once you have enough to not have to work for living expenses switch to doing just enough part-time to cover hobby expenses?
It is one of my greatest hope for everyone to be able to achieve this. It would shift the workplace dynamic so much that employers would have to work harder (beyond pizza parties) to retain employees since no one would blink an eye at the thought of resigning on the spot.
OTOH some have a lot of money.
They work their butts off as far up as they can in a place like a NY bank, then retire, early or not and join the yachting community :)
Sooner or later they find out that a one-day fishing trip is more work than a whole week of employment was, and they need more than a week to recover.
So you end up with a yachting community with most of the vessels just sitting there most of the time :\
It's a common phenomenon in those communities because many of the participants are young (the E is for Early retirement).
The common way to get to FIRE, unless hitting the lottery or getting a crazy RSU payout, is to be super frugal with a high savings rate.
Then they get to retirement and realize that doing the amazing things like traveling the world requires a lot of money. Even many hobbies start to require money. Then reading books, browsing the internet, and playing games starts to get boring when it's your entire life.