Why? And can we get him back?
Well first I agree with your OP, even if you don't agree with my reasoning. When you look at last season - who did people want as our captain instead of Maguire? Who was playing like the captain at United? It was Bruno.He was our main man. Everything was running through him just as much as for him. Playing centrally almost as part of our core, hard working and all.
For me this changed when Ronaldo entered.
Do you remember how Bruno Fernandes missed the first penalty he took when Ronaldo was on the pitch. He looked a different player as he went to take it, like he was different player. He knew Ronaldo was there and was wanting to take/has history with the penalties.
Who do people want as a captain now instead of Maguire? It's turned to C Ronaldo rather than Bruno. Some people pick De Gea because it's wrong to pick Ronaldo over Bruno or vice versa.
Our main man is now Ronaldo. Our tactics have turned to getting the best out of him than last years - getting the best out of Bruno and for him to get the best out of everyone else.
People are now talking about how Bruno's not passing well (because now he is heavily perceived by his passes to our central striker), for losing possesion, not assisting or playing like he used to. No one complains about Ronaldo losing possesion with a first touch that bounces off his knee though.
Why do people want Bruno dropped unlike last season? I said this in the Ronaldo thread- we didn't play like a team that played with a sole number 9 requiring the creativity from the rest of team last season. Did Cavani or even Martial need that? We instead had inverted forwards, a ST who tried to hold up play and play interlinking passes inbetween the IF's, all trying equally to score a goal whilst Bruno would either be trying to also score or assist them.
Our attack has gone more simplistic, turning from a 3 forward team set up by Bruno - to a team that all now tries to get the best out of one player in Ronaldo.
Ronaldo is now the main man at United and Now Bruno plays like how he does for the Portugal, not how he did with Sporting Lisbon and United where he was the main man of our team.