This has bothered me, too. Especially because the major flaws in the augments (as pointed out in "Space Seed") are that they are overly aggressive and overly ambitious. They can't help it. Spoiler: Speculative answer He might care about them as loyal allies. He was the "least brutal" of the tyrants, remember. That said, I can't imagine how he would stoop as low as he apparently did for so long and not find a way to use his superior intellect and such to free them a lot sooner. How could someone who can't control his aggression and ambition be subservient to Starfleet for more than a day without being unable to take it any longer?