Fact: Conan was canceled mainly because of his ratings. They were less than half of what Leno was getting and NBC wanted to put a stop to it.
That's an incredibly simplistic view of the situation, and you're ignoring all the context. Conan's ratings were low because A) he was re-building an audience, just as Leno had to do when
he took over
The Tonight Show (as has been said many times, he never beat Letterman until he lucked into Hugh Grant), and B) his lead-in was non-existent due to no one watching Leno's show, and the carryover audience to local news being completely eroded as a result.
I've seen people say, "You know, Conan didn't get higher ratings than
The Jay Leno Show until this whole thing started! It was time to bump Conan!"
The Jay Leno Show was in primetime. It's
supposed to get higher ratings than anything in the late-night field, which is a completely different animal when it comes to viewership. That it was getting only marginally higher ratings than Conan's
Tonight Show is evidence that no one really gives a shit about Jay Leno anymore.
This entire situation could have been avoided if NBC had grown a spine last year, and when Leno started making noise about going to another network, said, "Cool, see you later." Instead, NBC wanted to have its cake and eat it, too. It's incredibly short-sighted: Jay Leno is 60 years old. How much longer is he going to do
The Tonight Show? He won't do it forever. So when he hangs it up in three or four years, what's NBC going to do? Promote Jimmy Fallon?