"So few if any"? You must be forgetting about all the people who do useful stuff like filing bug reports, writing howtos, lending a hand on forums where the software gets talked about, writing and sharing scripts, plugins, modules, and other forms of add-ons, donating cash towards a particular application or documentation project, and hell, even in some cases *gasp* coding applications. Yeah, I know, it's easier to pretend that not one single person actually puts any effort towards anything and that everyone's just a freeloading ingrate unwittingly applauding their own destruction as they vaccuously wave their FOSS pennant and take the willingly-offered fruits of other people's labors, but no matter how many times this gets pitched, the end-times trumpets don't sound.
People keep making stuff and giving it to other people on the terms they decide, because that's how they want to do it. If you want to write and application and charge for X, Y, and Z around it, nobody's stopping you.