Vampires don't have working brains, though. A vampire's flesh and brains are dead meat, moved like puppet limbs through the negative energy that serves as the only connection between the body and soul in that undead state; think of the negative energy as the puppet's strings, and the soul as the puppet master or the handle part that connects the strings. Their minds work purely from their spirit, not involving any fleshy parts to link their mind to the physical world and restrict it through physical/physiological means. Enchantments probably utilize that biological component; magically interfere with this part of the brain, or these nerves, and you get such-and-such effect.
Without a physical component linked to the immaterial mind of the vampire, the enchantments have no direct way to interact with the mind; to do so would require interacting with the soul itself, which is the province of high-level spells like Finger of Death; lower-level spells can only seem to interact with the soul indirectly, through channeling negative or positive energy to bombard or restrain the spirit. If enchantments were to be made that could affect undead, they'd likely be 4-5 spell levels higher than any equivalent enchantments for living creatures. I.E. Charm Undead might be a 5th or 6th-level enchantment, probably only available through expensive spell research; Hold Undead and Undead Suggestion may be 7th or 8th-level enchantments; Undead Geas or Dominate Undead would probably be impossible to create, or simply epic-level.
Part of what balances out the immense utility and versatility of Enchantments and Illusions is that they're ineffective against a few kinds of monsters, i.e. constructs, undead, oozes, vermin, and such. Necromancy covers a bit of that ground with undead only, as does clerical turning/rebuking, and through different means (controlling or adjusting the movement, intensity, and such of the negative energy that animates the undead).