The problem is how few games make playing as a necromancer villain viable or even fun. Playing as a villain is usually just being a dick for absolutely no benefit, and almost no game lets you play a proper necromancer creating an army of the dead.

The Pathfinder CRPGs (especially Wrath of the Righteous) are the only ones I can think of off the top of my head to do it right. You can turn the entire country into an undead hellscape, and even turn the good advisors into undead to ensure their loyalty rather than missing out on a bunch of content.