Maybe because he was expected to clown on Bonnar?
I have been paying attention for the last six years. He's the GOAT and he was expected to destroy Bonnar. Bonnar hasn't beat anybody notable in his entire career (please tell me who Bonnar has beat). Silva beat up on a can... that doesn't make for an exciting fight. It means Silva beat up a can.
That's not exciting.
Yeah he was expected to beat Bonnar, I'm sure the majority of the people who watched the fight expected it to be a one side beat down. For me it was an exciting fight as you get to see Anderson Silva show case his skills. Here is the scary part, Bonnar has faced: Jones,Forrest,Evans,Machida,Coleman,etc...sure they whooped his ass, but none of them made it look as easy as Silva did. Even if he is a can, nobody makes beating up a can look effortless as Silva.
At the end of the day watching Anderson Silva fight is an event, as I don't think there will even be a fighter like him again.