Here it is- there is a difference between performing for an audience (as in getting feedback from a live person) and performing for an "audience" (as in, tailoring your performance for the audience that you know you will have).
Easy examples-
An actor is on the set of a movie. He is performing for an audience- the eventual audience in theaters. These performances will be different than just a performance for an audience that is live.
Or a trial attorney- he has to perform for many audiences; his client (who is paying him), the jury (who will decide the case), the judge (who will rule on issues as the come up), and the record (for any appeal).
Here, the idea that these performers, these artists ... who make their living performing in boxes with an invisibile audience (voice actors) are unable to perform as streamers seems ... not very well founded? In fact, they've said the opposite:
As voice actors, I think we bring a very thoroughly honed imagination to the game. We spend a lot of time in nondescript recording booths creating something out of nothing. There’s no stage, set, or even other people to work off of. The job requires you to play inside your own brain-powered, Star Trek holodeck, painting the surroundings and circumstances around you with your mind. Add some rules and dice, and you’ve got D&D. Now we get to take all the same skills we’ve been using for years in the booth, and create our own story, in the moment. And the thrill that generates is addictive.
-O'Brien
What all of us bring is our ability to imagine, and I know that sounds kind of lame but as a voice actor that’s what you’re doing all the time, creating these huge scenarios in your head so it makes sense that you’re making these zany voices in a tiny booth all by yourself. So the minute we’re in these scenarios with each other all of us can picture where we are and we’re constantly … it plays like a movie in my head. When I think of memories of our campaign I don’t see it as us sitting around a table, I imagine these grand shots of our characters going on missions, and I think that may be it. A lot of us have improv training, so that also helps.
-Bailey
Which just goes back to the original point. The reason they are so good is because they are performers, and they are used to this kind of performance. It's quite amazing.
EDIT- ARGH! Kinja'd by
@Charlaquin