Dude, where did I say that was the only reason? It is one argument that you were overlooking/denying. You need a way to distribute a virus, and that's harder with a 1% market share than with a 70% market share.

Anyway, if linux servers are so secure, why is it called root kits and not administrator kits? There are different threats for different systems. Since Linux boxes have a high percentage on web servers and a low percentage on desktops, the threats towards Linux boxes have a different focus than Outlook viruses. On Linux, there are worms too, bots and egg drops and what not. Any system that is online, needs to be updated regularly, and it's always a struggle against the time.