There are reasons.

Reason  1: ICO's exposed Ethereum weakness.
Solution 1: PoS / Casper.

Reason  2: The fraud happen on G-DAX with $0.10 price for ETH
Solution 2: Stupid traders learned their lessons.

Reason  3: Fake news about death of Vitalik the founder of Ethereum.
Solution 3: He took a photo with latest block number to show he's alive.

Who had benefits?
The ones who cashed out
Investors that buy now when price low

Losers?
People that got panic and sold with lose.

In the folowing days you'll see major corrections