I can only guess, but I'd think all these hardforks have something to do with it. I think a lot of people are beginning to lose confidence in the project. We had the DAO debacle, then the hardfork, then the split with Ethereum Classic, now it seems hardfork after hardfork to try and repair all the damage from the original hardfork to stop the DAO hack. Just my observation, although I respect the work Vitalik Buterin does on the project, and the coins real potential, I haven't been a big fan since the DAO debacle.