There is always a reason for prices to fall. A famous investor may have talked about the crypto coins negatively, crypto coins in any state may be banned or a large exchange can be hacked. So I don't think too much anymore 
We cant question why it always like these, in fact since the beginning price fluctuations already exist and as we recall, the current prices are totally far by then.The popularity of crypto turns into some people having a bad interest on it, and they'll just do scamming and hacking accounts for the seek of their own which could ruin the entire community.