Time of year?
Probably. We generally get a lot of new members around this time of year, and newbies are more likely to disinter zombies. People who have been around for a while may find 'em, but they’re more aware of the expectation that they be left dormant.
A fresh infusion of braaaaains is sure to stir the up!
That doesn’t explain why so many are still animated.
It’s a forerunner to The Apocalypse[SUP]TM[/SUP].