Patreon supporters are paying for at least one full-time developer. But one (or two or three) people are going to have a hard time bug-fixing and developing a project of Godot’s size all by themselves. Godot is also open-source, so contributions by people (not just those being paid via Patreon) are welcome (and, due to the size of Godot, necessary).
If you’re unhappy with that, then stop supporting the Patreon, it’s that simple. Or start contributing a lot more, if you want all the people developing Godot to be paid.
The next goal of $10,500 is also not that much when you consider a full-time developer should be making six figures ($100k+) easily.
Juan must be supplementing his income or living way below his means, and game engine development is way more hardcore than what I do.