For two consecutive days, Bitcoins fell late at night. There are many rumors on the Internet, some people say that the exchange joint bankers, institutions, a hanging of retail investors. Others say they are preparing for big organizations to come in one after another. But in any case, retail investors are innocent.
As you said, there are various potential reasons. I don't think it's retail investors, bankers or institutions, though. I got to mention that I am not a conspiracy person, and this might explain why I reject the rumors you've mentioned. I believe it's a combination of factors like natural volatility/correction after a long time of $9k+, Bakkt launch, a big transaction on Bitmex and some other things. Not to mention that these can be considered the primary reasons, but the secondary (in terms of chronological order) reason is almost always panic selling, so it's the community to blame, really.