Robinhood options being sold off+ delta-hedges unloading + I suspect an opportunistic attempt at <$820 for the MM's
What I don't get is why this wouldn't be counteracted by those mythical benchmark funds gobbling-up the lower prices, but volume is dreadful.
I agree, and I think the answer to your question is that the benchmark fund managers are sitting out the dip, wondering how low it will go. When there's a clear recovery, they will start buying again. They really don't understand the usual Friday afternoon push-downs by the options sellers. As you and I know, by Tuesday, there's a good chance we see a gap-up on open and they've lost their discount for buying.
The other consideration is that we've seen progressively lower volume this week compared to last Friday's. We're likely seeing some of the funds reaching their quota of TSLA shares, so there are fewer buyers as we progress onward. Fortunately, with ER on Jan 27, the event will spur on additional buying by a different set of investors or traders for positioning prior to the ER.