Yes, lets bring every robot that died in the first film back to life and make their deaths loose any meaning (when there is any).
Megatron is brought back to life but the way they bring him back makes it limited at best. Without any other pieces of the Allspark except the one Ravage and the Insecticons steal from NEST's base, bringing the other dead Decepticons back to life is impossible. If they could just revive Cybertronians at will, Jazz would have been brought back long ago. And Prime's death wouldn't pack the punch it does. I mean, half the movie revolves around Sam trying to find a way to bring him back from stasis lock. So bringing Blackout back, although he was awesome, would make no sense at all. (Though having an almost exact duplicate around doesn't make much sense either).