Marketing.
Bitcoin is sexy. It's Silk Road and Darknet and Randomware and Chinese Mining Conglomerates.
Ethereum sounds like a Greek morality tale. Bad marketing. But don't worry, Ethereum will get there eventually.
I mean, hell, "Walmart" sounds like a place that sells faux wood paneling, but look where it is today.
I agree, a good name is definitely important in establishing a reputation early. While I'm not the biggest lover of Dash, their name is, in my opinion, one of the best, at least compared to something like "Bitcrystals" or "Decred". I think devs are becoming more aware that you need to design your coin with at least some degree of accessibility in mind, and Dash have done an excellent job of this.