Speculation is another reason. I got 1000+ while the were closer to 0.001 and now they're closer to 0.004; I also bought some at 0.007 before they dropped. Of course the same kind of speculation can be done with Bitcoin, but the variance and current increase in popularity may attract speculators.

Used to also be good for CPU mining. They're still better than SHA-256d currencies for CPUs, though. I think GPU hostility probably made more laypeople eager to mine and adopt it but that's just me.