Mainly as a hobby project, as far as I can tell. The overwhelming majority of categories of "long term investment" are either completely mathematically impossible to deliver on the promises (this is where most of the crypto investors are), or have already proven themselves to be complete crapshoots where you either win big or lose big (this is where the people "investing" in things like beanie babies and trading cards are).
There's no investment that can gain value indefinitely. There's some that will probably gain reasonably steady value for the length of your or my lifespan, but they're few and far between, and usually rely on active management, government backing, or both.
> Most people don't do anything with index funds either
It's rather the point of an index fund that those are actively managed. You don't just type "i want to invest" into your Compaq Presario, turn the computer off, and come back twenty years later expecting to have double the money.