Because it isn't even good.
Dodge? You like dodge roll a monk, they have plenty of dodge. Guess what. They're considered the worst tank class atm. How is dodge better than on demand 10% physical damage reduction from a dwarf? Or even draenei heal that scales with vampiric blood?
Movement speed? You want one, roll a worgen or a goblin, the on demand mobility is better than minuscule passive.
Haste? Roll a gnome, more reliable and you get extra 5% runic power on top. Or goblin again, you get it paired with nice mobility burst.
Blood elf for extra interrupt and on demand resource is already considered BIS racial for every class that uses a resource.
Passive racials are only better in one occasion. That is, when the player doesn't know how to optimally use actives, he'll be better off with passives he can't mess up or forget to use.
Tbh, you want a horde passive racial, roll an undead.