1) Few if any of their ports came out simultaneously with their Windows cousins. Even the quick turnaround of the Tribes 2
port was slow, and even though id did their own port of Quake 3
, Loki's lack of resources meant that they couldn't get their products to stores in time.
2) Most gamers don't run Linux. Sure, many do but not the critical mass needed to sustain a company.
3) Most Linux gamers were willing (begrudingly) willing to reboot to Windows to play games, meaning they would buy the Windows CD (not put out by Loki) and then patch later.
4) Most Linux users use it for servers and such, not for games.
5) Many (not all) Linux users don't want to pay for software (thus the free OS, the free graphics program GIMP, the free office suites, etc.)
6) Most software retailers didn't want to carry the games because no one buys them (though part of the reason Linux gamers are few is because no one carries Linux games)
7) Loki required (or just wanted) binary patches to their software, so few developers wanted to work with them
The list goes on...