I agree with the actor/player issue, but I view the WoTC live streams differently than Critical Role and Th Acquisition Inc sessions. With those productions it is obvious that the goal is to entertain an audience while the goal of the live streams is to just play D&D. Sure, they could try to achieve both goals (and to me, Critical Role does seem to hit both goals) but I'm pretty sure they want to make sure that the live stream games are more representative of games that most folks play in their own living rooms.
I'm not sure why they decided to do that, but from my own experience, when I feel too much pressure to perform and create the perfect session (as DM mostly but also as a player) the planning and running of said session becomes more like a job and less like a fun experience. I think the live streams are more about just playing just for fun.