Somebody made the point--and I wish I could remember who--that the Ancients were just being really, really passive-aggressive. They didn't mind Daniel stopping Anubis, and they'd even give Oma a hand in their own totally unhelpful way, as long as they didn't have to intercede directly. By keeping Daniel there as a catalyst between Oma and Anubis, they get to be *sort* of good guys without losing face. And the memory thing...yeah, that was weird, but who knows how much he actually remembers, or how much of it the Ancients still care about keeping secret?