This is because the vast majority of "FOSS advocates" are really "i dont want to pay for stuff" advocates - or to put it differently, what they like is the "Free as in beer" with the "Free as in speech" being a convenient excuse that also allows them to be preachy about their choice despite its shortcomings.
All those people who work in IT / development etc and advocate FOSS, do you really think that they couldn't pay for commercial software if they wanted? I certainly could.
It isn't about "could" is about "would", notice that i wrote "i dont want to pay" not "i cannot pay". After all that money you save on buying XXX is money you can spend on something you actually value.
