The same people who have been writing it in the past. And who said there are no means of making money? You're just assuming something which isn't true just because you can't come up with an explanation.
Who are those people? Most are paid or sponsored by corporations.
Well just let them continue to do so, then?
So either open source developers have to work for and enrich corporations or work on the side for free?
Why should software development be any different than any other profession where people get paid for their work?