>Why should the resources not come from the companies extracting the most cash value from open source?

This is easy to answer: Because most/all those open source writers explicitly said it's OK for the users of their software not to provide them cash for it. If I openly say you can use my stuff for free, and then later come and say you are morally obligated to pay me because you made huge profit from my stuff, then my integrity is compromised.

It's totally fine to say "I will no longer respond to support tickets for free", though.