Because to have the free stuff, you need to dev it. To dev it, you need money to eat while you dev. So they ask money to live now, while they can code the free stuff.
That's not to say there is something wrong with it. It just seems confusing at face value.
I'm not really sure why the idea is such a foreign concept to the point where you need to insinuate that I think that Free software "falls from the sky" or some such nonsense.
That's a new one. How does someone getting making a living while developing open source software mean "everybody loses"?
You can, however, do it as a function of your work for your employer. Almost all of today's viable FOSS started like this, because it provides the financial security and moral support you need to bring a FOSS to maturity.