Except for RuneScape, Elder Scrolls, MAID, RAW DnD (multiple editions), Vampire the Masquerade, GURPS, and many more. Its a trope that I think originated from Warcraft (really unsure about that answer). But not really many RPGs do that according to their rules explicitly.
It started in D&D 2.0 for certain, might have been in 1.0 but I don't remember. That predates Warcraft by a few months....
Also that's the way it worked in 3.0 D&D. You had to cast "Cause [Intensity level] Wounds" to heal Undead. I dunno about 4th, but my friends that play 5th run it that way.
Except ChronoTrigger, Final Fantasy, Kingdom Hearts, Secret of Mana, Star Ocean, Phantasy Star, Panzer Dragoon Saga, Persona Series, Xenoblade, Pokemon, the list is much longer of those that don't than those that do.
I don't believe your claim is properly sourced with hard data BUT you're on the right side of history
Undead are made with eviiiiillll magic and healing hurts them because it's good magic.
Now, if want to go full "magic is a science because you get predictable results from consistent inputs" and start talking about reversed polarity zombies...