I’m certainly not ignoring the lore, I’m in fact focused on exactly the lore as it relates broadly across almost everyone that turns undead. No one escapes being turned without also becoming something different, mind, body, and soul. Undeath make you darker. Even the few edge cases that are largely anomalies in the grand scheme of things, wind up significantly darker than they previously were in life.
This is not to say that you do not retain your previous memories.
But put yourself in the shoes of the newly risen Undead.
You come back to life as an Undead elf. Your previous allies are now committed to killing you on sight. Not because you are by definition Horde. But because you are Undead, and in their eyes you are now a monster that needs to be put down. Is it rational for you to go back to them?
This is how every single newly risen undead that retains sentience comes back.
In the Horde, the Forsaken exist, and there’s a place for you. On the Alliance, Undead = kill on sight, unless you are a Death Knight. Outside of the Ebon Blade there are pretty much zero instances of Undeath being tolerated on the Alliance.
Maybe that changes in lore some day. But today it’s not the case.
Either way… Undeath makes you different. Living in Undeath in WoW is very akin to IRL living with depression. You are still the same person. You still have the same memories, the same allegiances, the same philosophy, the same basic “you”. But you are changed nonetheless. The chemical neurotransmitters in your head don’t function like they normally do, and it leaves you experiencing agony, pain, and suffering more easily, rage and anger more easily, and it saps you of your ability to find enjoyment in things. It changes how you experience the world, for the worse.
I have bi-polar disorder IRL, I have been to the pits of despair at my worst, to the point I lost my sense of smell and with it taste, and any food I ate left me wracked with pain in my stomach like hot nails grinding their way through my insides. My color vision got washed out like the world had been run through the wash too many times.
It was miserable. And Undeath in WoW seems to do something very similar to those afflicted by it.
It’s not mind control. But it does make you and how you act, think, and experience emotions different.