OK - so how are the antispyware writers buying groceries?
Most of them do it as a hobby. You don't know young (15 to 30s) male computer geeks like I do. In their spare time, they write 'better' compilers or train for obfuscated programming contests - or, for the recognition of their peers, write freeware. It's fueled by pride, not money, most of the time.
Plus, "I wrote Spybot S&D in my spare time" looks really, really good on a resume.