my observation is that this drop was due to manipulation and not much else. it started by CSW's lies about dumping bitcoin and continued by whales taking advantage and dumping bitcoin.
the situation was also perfectly ready for such a drop because of the stability which made everyone bored and most traders to leave the market.
I would add something to this: some speculators that bought in with the hope for good news from BAKKT may have heard the news early and profited on the BCH split to sell. (They'll buy back cheaper and will be ready in January for BAKKT again.) I don't say that ETF and BAKKT are serious subjects, however I expect some may speculate around it.
And I think that there are other causes too, including the rather new troubles the Chinese government did to the miner companies.
So while my opinion is also that the current price drop is heavily linked to speculation, I think that there are multiple speculation "vectors" that combined this time for the worse.