In all seriouness though, has anyone kept a tally on all the Cthulhu, steampunk, zombie, etc., decks? I honestly want to know how many decks cover the same themes.
You REALLY want to know? I had no idea you were a masochist!
My answer to your question is "Way too many!"
Haha, yes I really want to know!
Kickstarter lists eight successful playing card projects. This doesn't count non-standard decks for special "zombie" games, nor does it count the failed projects.
USPC lists three "homegrown" decks, all zombie-themed. There are others that are fringe-zombie themed, but not quite - the Anne Stokes/Alchemy 1977 decks, the Skull deck, the Club Tattoo deck, etc.
Eleven and counting. Have no idea what came before these eleven, if anything, that was zombie-themed.