$2 isn't really the incentive to have a youtube channel though. People enjoy making something and sharing it with the world. Most people who do X as a hobby don't make even $2 for almost all X: art, music, fishing, whatever, and yet they still do it.
You usually have to go up to "serious amateur" level before you make even token amounts of money (which still doesn't cover your tools much less your time), and 1k subscribers for a video hobbiest is a low bar for that.
Lots of open source is either people doing it as part of their job, or people doing it as part of building up a portfolio to get a certain job.
But of course there are more intrinsic motivations like wanting to give back to the community, practising their hobby, etc. Those would be equally valid reasons to make youtube videos.
Depending on how philosophical you want to get, there'll be people who derive pleasure and purpose from sharing what they know or building something that is enjoyed by others. There'll be people who gain pleasure from being known for being helpful/useful/knowledgeable or even being recognized at all. Even if we can't call it altruism that's not necessarily a bad thing. I guess I just feel that there are, and likely will always be, plenty of incentives for people to create and share online besides financial ones.
You usually have to go up to "serious amateur" level before you make even token amounts of money (which still doesn't cover your tools much less your time), and 1k subscribers for a video hobbiest is a low bar for that.