It is true about the interest rate, but I think there's another reason standing behind the crash: most of Bitcoin is focused in hands of rich people, businessmen, companies and they're manipulating the price. I have no proof for that, but it seems logical to me: even though BTC is decentralized, most people weren't able to afford buying it, when they first heard about it, so they have 1-2 Bitcoins maybe, the ones that new about BTC from the very beginning probably bought more and now they're rich, and companies - even they got to know BTC when it was already valuable they could afford buying a lot of it as an investing.