eek that does sound and look terrible I was just at the North Carolina Zoo last week and their exhibit looked awesome! they had 2 tanks - one with panamanian golden frogs (with a mating pair!) and the other with azureus, tincs (a black and yellow morph... maybe alanis?) and leucomelas.
I just went to the National Aquarium in Baltimore (where I live) and they had somewhere between three and five dart tanks. They were pretty large, about 75 gallons a piece and were species-specific, if I remember correctly. Two of the tanks weren't, though. One had probably 3 different thumbnail species in it, and one had a tree snake. Overall, they looked okay, not great. But the general public will always be in awe when they see these beauties, not knowing that any bad husbandry techniques are going on.
It's a mixed bag. On one hand, you will always have people who want to do the same thing, and will say "oh, well, such-and-such zoo does it, so it must be fine! they're a zoo!" But, on the other hand, the zoos need to create "startling" displays for the public. It brings in the crowd, not to mention raises awareness of these frogs. The last thing a zoo wants is to have these big, gorgeous tanks (okay, so the ones here aren't big, or particularly gorgeous, but you get the idea...), with one species, and have visitors leaving bored and feeling that the zoo is a bit lackluster.