"Classic" vampires have always been a bit sexual, but unlike the whole Twilight crap, it wasn't treated as romantic, and served to underline just how twisted they were.
Remember that they were pretty much this idea of a twisted monster that pretended to be human, an action that served to play with the human mind, which was their main focus. Their whole purpose was not to kill you, but to damn you. They went about casually twisting emotions about, be it feelings of romance, anger, paranoia, or just plain discomfort (to get a good taste of just how this plays out, go read the first section of Dracula).
In other words, vampires are creatures based as much in physical fears as in psychological (especially since one of the biggest concerns is that being turned into one is effectively losing your soul).
Zombies (at least the idea of shambling or running corpses acting on instinct rather than voodoo magic) are actually all about the physical scares. Sure there's a bit of the psychological when you involve "infection" into it, but that's only limited to the idea of hurting someone with your death.
Zombies are focused on killing, not on causing problems for the protagonists' mind. There are no zombies (of the type we're discussing here) who are magnificent bastards that work the protagonists to make them fall, so there's no reason for seduction.
Now, one thing that's funny is that originally, the roles of these two undead were actually reversed. Zombies were all about the soul/spirit and dealing with fighting something invincible while trying to keep faith while vampires were about survival.