Main reason is because whales want to get into bitcoin. Capital controls are tight in certain countries like China and Korea and therefore people are prepared to take a risk in assets that allow them to get away from government agencies that constantly monitor their wealth. I disagree with people who say that it's just hype and speculation. I believe that it's actually people discovering that bitcoin is a good way to store their wealth, and actually buying into it.

Proof? Korean and Chinese btc prices are always on top of the USD price because of tight money controls. I know that the korean markets have slowed down but if you look on localbitcoins the chinese buyers/sellers still trade at a high premium of 10% at least. And the USD rate is a bit lagged imo so it'll follow the trend of these exchanges. I'm not saying that none of this is speculation, probably a lot of it is. But it's not all speculation either.