Because Mo was and is a lot better than Ed. The Ed we saw last year and this year, looks raw still. Not saying I don't want him up, as I do, but you act like he is ready for primetime minutes and I don't think he is. Right now, sheltered minutes are probably what would be best for him. He has lots of skill, but he also has lots of little things he doesn't do right. You can rag on the NHL vets like Maatta all you want, but they are solid, where you know what you are getting. Ed right now would be a mixed bag, and expecting any NHL coach that has their team in the playoffs currently to want to switch to a rookie is not something many NHL coaches will or would do.
When Mo played his first game, we could see this is a big time player, I haven't seen that from Ed yet.
Ed isn't exactly ripping up the AHL offensively either. If he was top 5 in offence from Dmen down there, I would get the complaints, but he is 23rd in offence from Dmen, and still has lots of space to grow defensively.