From what I can gather it seems to be caused by numerous, but drastic factors ranging from Exchange outages/downtimes to The New York Agreement and confusion over the future of Bitcoin, proposals made by major pools and such to political developments (do not start an argument over politics just discussion related to market).
Here is a timeline provided by BitcoinMagazine regarding important times regarding Segwit activation and The New York Agreement proposed integrations.
Here is a detailed analysis by BitcoinMagazine discussing the implications of integrating Segwit2x into Bitcoin which is one of the factors of The New York Agreement: Segwit Acceptance - Bitcoin Magazine
Here is a statement from the bitcoin.com team regarding The New York Agreement:
This agreement being the first such proposal in nearly two years to find support from major industry players on both sides of the scaling debate, we felt that to remain opposed to this development because it wasn’t our ideal outcome would only prolong Bitcoin’s capacity crisis and contribute to even more division than there already is. In our view, the long term health and survival of the Bitcoin network is of greater importance than being the “winners” of the block size debate.
At the same time, we have not forgotten that a previous agreement of this nature (with nearly identical terms) not only fell completely flat, but actually widened the divide in the Bitcoin community and prolonged this nasty debate by far longer than acceptable. We remain cautiously optimistic that the agreement made in New York this week may be able to bring an end, or at least temporary relief, to the existential threat that faces Bitcoin today. We wish to emphasize that while this is an agreement, it is not binding and we are not particularly attached to it. Should we feel that this agreement is not being acted upon in a timely manner, or if it begins to resemble another excuse for extended stagnation, we will quickly and emphatically withdraw our support and continue our efforts towards scaling Bitcoin on-chain, in accordance with the design of the system as outlined in the Bitcoin whitepaper.
What are your feelings as to why every cryptocurrency is varying so dramatically lately? Is it mass panic? The burst of a bubble? The end of an era or just a new opportunity?