With the amount of transactions bitcoin currently has >300k/day, a rollback is almost impossible. Planning a rollback and getting everyone to agree with it would take some time, and what would you do with the >300-2000k transactions that were confirmed before the rollback?
There is a lot of money moving in bitcoin. How can anyone justify cancelling than many transactions?
Imagine. You sell your car for bitcoins, wait for it to confirm hand over your car and then the next day you don't have your coins anymore 
What would that do to the reputation of bitcoin?

Maybe, if there would be a HUGE theft that would be noticed immediately, but that would have to be REALLY huge. I cant imagine such a thing happening anymore.
When a rollback was done bitcoin was a lot of smaller and there weren't as many transactions then. And the bug would have destroyed bitcoin if it had not been fixed. (someone created ridiculous amounts of new bitcoins from nothing. IF I remember correctly he created hundreds of millions of bitcoins...  so something had to be done)