Easy. Because:
A.) I didnt say yaw or pitch rate were irrelevant, just less so these days. There is a growing trend (in western doctrine) away from having the pilot do the hard maneuvering, and towards having the weapon system do it instead. That said, a B2 is obviously too cumbersome in both speed AND maneuverability to deal with those "oh sh*t" scenarios where Murphy's Law takes effect.
B.) "Laser turrets" can still be saturated. They are not a panacea, but they will almost certainly be a game changer in the A-A arena.
C.) B2s are horrifically expensive. The USAF simply could not field enough of them to cover its global commitments/interests. Nobody else would be able to afford them at all. The fleet would also have zero room for attrition.
D.) The USN couldn't fit them on their carriers. Not much more to say here really.
E.) Turreted lasers are only likely to function effectively in the WVR or near BVR range in their immediate future due to their energy demands. 6th gen aircraft are probably still going to need to be able to use A-A missiles to some degree in the air superiority role, and thus confer upon them all the kinematic advantages that a B2 or similar is simply incapable of doing - particularly in BVR combat.
