You raise an interesting point. No airline wants to pay for it, and no regulatory authority wants to mandate it. Yet, I've never met a pilot who would not like to see AoA in the cockpit. When it comes to safety, why are pilots not able to demand the installation of certain equipment?
I can envision a surgeon refusing to operate unless certain safety nets are in place. Why do we allow our bean counters to say that something is too expensive? They're not the ones trained to fly, we are. Shouldn't WE be the ones demanding the installation of AoA indicators?