Yeah, but...it HAS canceled itself, really. At least in any form that resembles science fiction, basically. they are now the "****ty movie, Reality Series, and Wrestling Channel."
I see this happening with most of the "themed" channels that came into existence in the 90s. I mean, with the exception of something like Travel or Food networks, think about the channels in question.
The Learning Channel? Pretty much just crappy reality TV shows that don't actually teach anything.
The History Channel? See above. Oh, and the occasional BS like "Could ancient astronauts have built the pyramids?" And sometimes some WWII stock footage shows.
Discovery Channel? See above.
These days the only distinction between these channels and, say, VH1, E!, etc. is which reality show is on which station. So, don't go looking for "The Real Despicable Useless Housewives of Rich Morons" on VH1 because that's on E!...for no apparent reason. Don't bother looking for "Kate Gosselin is a Fame *****" on VH1 because it's on TLC...again, for no discernible reason. Don't bother looking for "Ice Road Lumberjacks Who Eat Crabs" on TLC because, again, that's on the History Channel....and we're not really sure why.
Some channels have avoided diluting their "themes", but they ALL have reality TV shows now. It's a simple question of numbers, ultimately. Reality TV shows are DIRT cheap to produce, and they fill up air time. Plus, because they're cheap to produce, production can all be done "in-house," which gives your station total control over the show -- including licensing and DVD rights. THAT means you get to shop the show GLOBALLY and ALL money generated by it comes right back to you. By contrast, if all you're doing is licensing ST:TNG reruns, sure you can get eyeballs and ad revenue....but that's it. The rest of the money is going to Paramount.
Even if ALL you're concerned about is ratings, with so many channels competing for eyeballs at the same time, it's not surprising that they do this. Especially when other somewhat more general stations are competing with YOUR network, why would you stick to only a narrow demographic? After all, Ghost Hunters is going to compete with Haunted America or whatever on The Travel Channel, so why stop there? Why not compete with, say, Spike, by picking up Wrasslin'?
