It's not explicit that the good guys realise the shard can revive a dead Transformer ala Megatron, rather than a sleeping one (was that how they referred to Jetfire's state, i can't remember?) And even if they did, they don't strike me as the type of robots that would savage one of their own to revive the leader!

If they just revived Optimus Prime with the shard, it's likely that half the story would be totally different - why would they need Simmons? How would they introduce Jetfire at all, where would the mythology of the matrix come into it etc.