This drop in the price are based on confusion between Bitcoin and Bitcoin Cash.

The average Crypto currency speculator does not understand the technical difference between Bitcoin and Bitcoin Cash. They read in mainstream media about a Bitcoin war and they think it is happening in Bitcoin
I agree that many crypto users are confused with some many versions of
BTC, for most of them any coin which have
Bitcoin in name is just
BTC and this is big problem. But main reason for big price drop is just an opportunity for extra earnings, people loves forks because of free money - more BCH in wallet means more new coins after fork.
The positive side of the fork is that people who didn't bother to claim their BCH, have now more incentive to do so.
BCash destroyed coin days activity is going through the roof right now, which means that people are waking up coins that otherwise would have kept sleeping for years? In other words, there will be more BCH in circulation than ever before, and there will be more BCHSV in circulation than ever before. More supply + less demand = low price. These dudes are shooting themselves in the foot with this.
Let people sell Bitcoin down as far as they can, I'll happily take over their coins, and I'm sure there are lots of more hungry Bitcoiners happy to get rid of weak hands.
I guess most
BTC users claim BCH long time ago, but some will for sure do it now and probably some of them will become victims of fake wallets as always in such situations. Fake sites and wallets for BCHSV are ready, hackers just wait greedy and naive people to give them nice profit.
Some people see this event as tragic, and maybe it looks like that - but for the long term holders nothing has changed.