Silva is coming back from some serious setbacks and I think he is still trying to get comfortable. I think the next fight we see him in, he will be back much closer to prime form.
Seriously, this guy got KTFO in ridiculous embarassing fashion against The Chris (2012) after murdering people since entering the UFC in 2006...a 6 year run undefeated.
He did not want a rematch, he was glad to be knocked off the perch, just wanted to fight for the sport and not have so much stress of being the best, UFC pushed him and The Chris II was a brutal injury.
Add the rehab, potential to never fight again possibly, more stress, busted for PED's against Nick Diaz who he beat pretty easily IMHO, and we have a bit of a gun shy Silva vs Bisping.
Give him one, maybe 2 more fights and he will be kicking heads clean off again. I'm actually really impressed with BP's chin from this fight, he took a shit kicking in the later half.