There seems to be an assumption that you can either be: 1) spending money; or 2) doing nothing but sitting around. Surely that choice, if it was ever true, is no longer true. If my living expenses are covered, it costs me $0 in additional spending to do a lot of the kind of productive stuff I would like to work on if I had more spare time.

For example, I have 4-5 open-source projects that I would love to contribute to, and several ideas for projects I'd like to start/maintain. That doesn't cost much. There's even quite a bit of research you can do without much money. Obviously some takes money (e.g. maintaining a chemistry lab or HPC cluster), but lots of math, CS, and humanities research takes little budget; just time, energy, and access to a university library.

If anything, I find it a lot easier to think of ways to spend money on leisure than on work. It might be cool to travel to a lot of places, stay at nice hotels, etc. But that isn't advancing the productive part of my life goals; that'd just be a nice-to-do vacation break. The productive parts for me aren't capital-constrained.

If you are into research you can become a professor and get a tenure. No need to live on $20k. However if you want to be/stay as an entrepreneur you better spend some cache on things you don't want to do yourself.

That's an option, but there are a lot of downsides to being a professor, in addition to upsides. It's not at all a clean alternative to being an independent researcher; you're an employee expected to play a certain kind of game (which involves things other than scientific merit, like status/PR, grant funding, publication-counting, etc.).

But in any case, my main point was that you're incorrect that not spending money means sitting around on a beach doing nothing.