I know there were other reasons cited, but if you watch the couple of episodes before Orion Acaba left Critical Role he spent the entire time shopping. The other players were visibly irritated, even vocally so.
Call me a cynic but I get the feeling that this (along with his increasingly min maxy style of play, which was at odds wit the character led approach of the others) must have contributed to a parting of the ways. Much as I loved his character I found the game aspects (as opposed to the story) getting more and more intrusive. The show is better for his departure, I'm sad to say.
I think this underlines the comparative failure to engage that DCA has. Too much game, not enough story.
There's a balance to be had, for sure, but what others have said about needing people prepared to engage with the story first over the rules/game, is I think true. It would certainly make for better viewing; better viewing leads to greater interest in the game from its official source; leads to more players: and from WOTC's perspective more ownership of D&D as a phenomenon rather than watching G&S walk away with bragging rights.