The prices rises in the main 3 (BTC, LTC, ETH) must be underpinned by the Coinbase system. I reckon it's the main port of call for most peoples first purchase. When you couple that with the hysteria of recent weeks it is inevitable these 3 would rise. It's also therefore inevitable that it will fall when the FOMO is no longer present.

The difference with coins like Steem is that it is pretty much driven only by the community and doesnt really have the public attention.