It was a major screw up on McVay's part.
Rather than stick with the winning formula, he changed it to a much more conservative and deliberate approach.
The Rams O looked like they were operating in Quick Sand.....and that was partially because clearly Austin was not part of the game plan.
McVay wound up removing a major threat; the fastest, quickest playmaker on the team, even as a decoy.

What was the rationale? I don't know. Probably because McVay thought he had to be more physical. Also possibly had to do with the expected noise level.

But all Austin can do is run the play he's given, and play when his number is called.

I think Dunbar is an ill fit for this team. He is not much bigger than Tavon, but has nowhere near the speed or quicks. I think that was another mistake in Minny; playing Dunbar in the backfield instead of Tavon. You do give up some blitz blocking, but you also lose a playmaker.