If they do think that - and I absolutely do not claim you are wrong - Then it's through ignorance. Developers can just as easily distribute compiled binaries for linux as they can for Windows, and even encrypt them if that's what they want to do.

Because linux itself is free and open, it doesn't mean you can't run commercial software on it without it being ripped off. I mean, my work pays many tens of thousands of pounds for commercial software running on Linux, and it's not just licencing that stops it being spread.