because in 2017 BTC start hight grow up and there are many people notice BTC and they start invest BTC,and in 2017 there are many ICO day by day,you want invest ICO you have to buy btc and eth,with many ICO it make more people buy BTC,in 2017 is year of BTC
I think also that investors switch to invest in different ico's until now the price of bitcoin is already dump and they lost a huge profit from bitcoin for the big dumped was happen start january 2018.