Because you at least still had skeletons killing things for you. And that's on piss-easy difficulty with low HP enemies that you'll play for like 2 days on live, where unbuffed skeletons can easily kill stuff on their own before you can get your big damage skill ability ready. I tried a build with them sacrificed to free up ability slots because darkness builds have a lot going on as it is and getting 2-3 corpses to get the ball rolling is 5-7.5 seconds of channeling Decompose. Unless there are really weak enemies in a pack like ghouls (though, again, piss-easy difficulty with low HP enemies) that they will die from just a Blight and Decompose to speed up the corpse generation, that's rather atrocious gameplay. Maybe if the passive skill that gives lucky proc to generate corpses had huge increase to proc chance if you had skeleton warriors sacrificed that could go somewhere.
Though, fundamentally, a key class mechanic like the undead minions shouldn't require wasting ability slots to function, especially when there already is a separate sacrifice mechanic in it for when you don't want them around. The fact that the minions fuck off the moment you take the ability off the bar is outright moronic. Especially since taking other abilities off does not impair them in such a way and, for example, Corpse Explosion still works fine when getting activated by Blood Mist instead even if you take the Corpse Explosion itself off the ability bar and send it to Costa Rica.