It's my understanding that they monitored ratings differently back then. Had it been done as it's done today, it would have been shown that Star Trek had the demographics needed, and would have stayed on the air.
I'm not sure that would've been such a great thing, though. Already they seemed to be running out of ideas, their budget was being reduced, etc. It might have faded into obscurity if not for syndication.
Right, it's ridiculous to say you can't be a fan of both Star Trek and Star Wars. They don't even occupy the same genre niche. ST is space-opera science fiction, while SW is epic space fantasy. Each offers things the other doesn't.
I'm a fan of Star Trek, Star Wars, Babylon 5, and sci-fi in general.