The childrens zoo also doesn't have that many animals, besides Bird Landing.
I do agree that every zoo should have some native species, but not every zoo needs to make a major exhibit complex for them, especially when nearby zoos have already done that (Fort Worth, Caldwell, Cameron Park).
Plus, which one do you think would bring in more visitors: a North American exhibit, or a South American one? South America would definitely have more interesting species that people don't see as often. Plus we really do need a good South American exhibit around here as well as an Asian one.
I believe that the only places that have SA exhibits in Texas are the DWA and San Antonio. El Paso and Caldwell have SA sections too but El Paso's is for both North and South America and I don't think Caldwell's is that large or impressive. The DWA is great, but there are species it really cannot house effectively with the space it has.