The horror of the undead is that something like you becoming "other." Do you think a dirt farmer is more terrified of an ogre zombie than a living ogre? Ogres, on the other hand, are probably as freaked out by ogre zombies as dirt farmers are by "used to be humanoid" zombies.
Unless the PC's come across a community of ogres, they probably will never run into ogre vampires that can only turn ogres into ogre vampires. They are too busy terrorizing ogres to spend their time bothering humanoids. Plus, think of how little blood there is in a humanoid. It isn't worth the effort to drink one of them.
So, what about gnolls? I figure Orcus must look around the Abyss and think "wouldn't it be nice (for me) if all those fiends were undead?" There would probably be all kinds of nasty things bothering gnolls if the PC's ever found a city of them, but when it the last time that happened?