The Synods were meant to be railroad jobs which rubber-stamped the already-written AL but things didn't go as planned, starting with the outrageous interim relatio of the 2014 Extraordinary Synod, which caused an uproar.
The whole thing was a transparent, orchestrated attempt to endorse Kasper's "serene theology" which had already been incorporated into the drafts of AL.
The Synod has been a farce from the beginning.
At the very first one, in 1967, the Bugnini Mass was celebrated for the bishops’ approval. I don’t know whether it was a “dry Mass” or not. They rejected it. I think it was actually unanimous.
So, the bishops were simply never asked for their opinion again.