Why do you not donate to the causes?

In some recent threads, there were some implications and other statements that, when I recall statements from Fonality and freePBX people lead me to wonder: for those people that make money (regardless of whether it's your main livelyhood or an occasional paid project on the side) with "free" software and don't donate: why?

I can see that there are basically two groups of people that use trixbox et. al.:

1) hobbyists: regardless of your level of techical proficiency and/or experience, you are not using trixbox et. al. in any income-producing way. You have installed a phone system at home more as a hobby and/or to learn.

2) professional: regardless of your level of technical proficiency and/or experience, you are using trixbox et. al. to produce revenue directly (eg: a system-integrator/reseller) or indirectly (eg: you've installed trixbox et. al. at an office (home or work) that is the REAL phone system in use by that business).

For the sake of brevity, I'll set the first class aside. For the "professional" class of folks, there may be some that do not donate to the other people who have provided the software that the professionals are using to generate direct or indirect income. My question for those such people if they exist is: why? What are the cons that lead you to that decision?

I suppose there may be a sub-category here: I have seen a post where a system-integrator-type said he was doing to donate to freePBX a certain amount for every install he did. But what about the trixbox folks? What about the centOS folks? What about the mySQL folks? If someone is using the Mondo backup stuff, what about them? What are the reasons for donating to a subset of the projects you're using?

Yes, I do realize that this software is all covered by licenses that do not _require_ any payment(s) and in this specific case, we're not talking about shrink-wrapped software purchased from newegg.com, but if there are few people donating, doesn't that fit (indirectly) into a biting-the-hand-that-feeds-you category?

I can't quite figure it out. It can't be simple greed; if it were, system-integrators could simply increase whatever their bottom-line fee is and add X dollars that is ear-marked for the software projects. (Whether that X dollars is $20 or $200 is not the point, and whether the ear-mark is disclosed to the customer is not relevant.)

I REALLY am not making a judgement here, rather I honestly wish to understand.

*** --- >>> I also don't wish to see a flame-war start here for people that disagree with other people's values.

Thanks.