I'm part of several small/mid-sized communities where people voluntarily do sysadmin work so that the group can have some nice shared services, and that's to say nothing of the number of people I know running personal homelabs/self-hosting setups at decent cost just for fun. You could of course say that fun, maintaining something for friends you care about, or having a dream of less corporately locked-in software are all incentives, but they're not monetary ones.

Really, it's easy to get sysadmin types interested in this; the problem is that most people aren't sysadmins and don't know any. If you really wanted a business model out of this, it'd probably be a managed service that lets non-tech-savvy users spin up their own versions of this without learning the details.

> Without this, it will work --- in the same way that open source works --- without any guarantees or commitments whatsoever.

There are plenty of successful economic models around open source, and plenty of open source software is used in high-reliability contexts. What comparison are you trying to make?