Ethereum exploded in 2017 primarily driven by one catalyst: speculative demand for ether as the reserve asset for the Ethereum capital market (ICOs). As ether was necessary to participate in public token sales, demand for ether went up and as treasury teams of ICOs held ether, more and more circulating supply was removed from the market as demand increased. This is all fairly axiomatic, not mind-bending stuff.
More interestingly, given regulatory concerns over public token offerings, other alternatives have emerged to distribute tokens to a wide base. Historically, some of these options (e.g. Coinlist) have taken a rather conservative approach: working with teams that are raising money privately from venture capital firms.