I think there are multiple reasons for this crash, with the biggest factors being:

1) People who bought high are starting to lose all hope that ETH will get back to ATH range and are just cashing out whatever is left.
2) ICOs are taking out their profits and selling ETH for fiat money.

Both scenarios can really make the situation really bad really fast. People/ICOs selling urge more people to sell, what follows is this chain reaction like thing.