The AZA bases its species and program recommendations largely on what its member zoos want to do, not the other way around. Species that are already doing well in captivity, exist in large numbers, are easy to acquire and that zoos like having are prioritized - out of practicality and necessity. Conservation is absolutely a factor, but zoos aren't just going to drop their popular and easy to acquire, easy to care for ring-tailed lemurs for a rare Eulemur species that is more difficult to find, more difficult to care for, and is not as interesting to the visitors. It doesn't make sense for them to do so.
Also, keep in mind what I said last time - there currently aren't enough Eulemur to go around anyway. Breeding some of those species is difficult; it's not just supply and demand. It's hard to make a small, unstable population large and stable. I'm sure there are plenty of zoos that want blue-eyed black lemurs, but if the zoos that already have them can't breed them then how is anybody else going to acquire them? I don't think it's obvious at all that ring-tailed lemurs are taking space away from other species.