There have been quite a few zoos building new reptile houses in recent years, so I think they'd disagree with you on this one. I'd also say, while they aren't as much of "superstars" as big cats, great apes, or elephants, there are quite a few reptiles capable of holding their own, and are fairly popular. Some that I can think of include:I think for many zoos, they would feel that money would be better spent on something biogeographic than on a massive taxonomic building, especially as aviaries and reptile houses often lack superstar draws.
- crocodilians
- komodo dragon
- penguins
- anaconda/reticulated python/other huge constrictors
- bald eagles (and a lot of other raptors)
- owls
So there are definitely some marketable species that could be included in a reptile house which includes the birds!