I don't.
Ambrose: Hey, about you trying to murder me with a cinderblock...no worries.
Whatever, everyone has past beefs with each other that have been forgotten. It would be a bigger issue in a company that stressed continuity.
That doesn't make it okay. They spent an entire summer with Ambrose trying to kill him and now they're just going to make up? Even though they never really got revenge on him? That's bad storytelling. It's too soon for a Shield reunion.
Why not? Ambrose is supposed to be crazy. Guys have forgiven worse in wrestling.