Ask HN: Why don't more open-source projects charge for support/features/bugs?

I see a lot of open source hackers getting jaded by the vampire-like community using their libraries for free and then complaining like a customer. I know that some libraries have a donation button, but most people won't donate. I feel like if these open-source developers would charge for priority support, or put "bounties" on feature requests and bugs, it would become more financially viable for them to work on their open-source projects.