It certainly doesn't help that development and distribution on Linux sucks ass, so porting to Linux is a huge time-sink compared to porting to OS X. Unless you pick a specific distro and *only* support that, in which case the Linux fans who yesterday were begging you to port the software are now bitching that you built it for the "wrong" distro.
Then your support costs run up the roof, because even in the "correct" distro people can install the "wrong" windowing system or sound subsystem or what-not, which becomes a support nightmare. So you pay more to port, then you pay more to support the port, then...
when you're done, nobody buys the thing anyway because "information wants to be free" and, shockingly, a community based primarily around a free-of-cost OS and making their own free clones of commercial products doesn't like paying money for things.
This stalemate isn't likely to change unless there is a major cultural shift in the Linux community.