i would say the main catalyst for bitcoin's rise this year was people buying bitcoin to buy ethereum to buy icos.
if there hadn't have been any icos then bitcoin would be half or less of its current price and ethereum would be 20-30 bucks.
Most of the time this is true. But there are also many investors who just directly buy ETH to join ICOs. The thing is that Bitcoin is readily available if people are using fiat to enter into crypto. That is why many passes through BTC first before entering into ETH and finally the ICOs.