Which isn't the fault of Blizzard or their writers, rather, he was too busy dealing with small-scale domestic issues to really take any spotlight
Saurfang was against Garrosh from the very beginning(AKA the first person against Garrosh), before Vol'jin was even Warchief. As far as others being against Garrosh, so was Sylvanas.
A rebellion that Vol'jin was the figurehead of, but let's not kid ourselves, it wasn't Vol'jin's personality or political prowess that put that rebellion together. The Darkspear rebellion was ready to form at a moments' notice, under just about anybody, thanks to Garrosh.
You might not, I think the rest of us might have a pretty good idea though.