I’m not sure what it is about characters that… aren’t quite human, but there’s something incredibly appealing about them.
I’m not the only person to feel this way, either, as evidenced by the popularity of everything from catgirls (a relatively tame variant on humanity) to the full-on monstergirls found in something like the Monster Musume anime and its ilk.
Zombies aren’t traditionally something thought of as particularly sexy… but there have been a few successful attempts to combine physical attractiveness with rotting flesh over the years. One of these can be found in the Shantae series in the form of Rottytops, a recurring character who has been present since the first game.