It's quite sad how badly captive deer populations have suffered due to CWD restrictions, though I agree it is remarkable how many programs are still surviving. The fact that the Barasingha, Pere David's Deer, Southern Pudu, and even muntjac programs have grown is excellent news overall. I know muntjac in particular are often one of the species singled out by CWD legislation which is probably a bit surprising given how common they are both in zoos and even in the private trade.
Incidentally, CWD restrictions are something I was just looking into yesterday as well. Simply put, there are only 2 US states that have no written laws specifically referring to CWD. These are Nevada and Washington*, who, in general, banned the keeping of captive deer for seemingly unrelated reasons before CWD restrictions started being implemented in 2002. Additionally, there are 32 states that have some form of regulation that restricts the importation, transfer, and/or keeping of captive cervids to varying degrees of severity. The most common regulation I found was states requiring a 5 year quarantine period of all animals planned to be moved across state lines as well as for all other animals kept in the herd. The remaining 16 states in the US have implemented a ban on the importation (and sometimes even the keeping) of captive cervids to some degree. Some states only ban certain species (native species and all Cervus and Muntiacus species tend to be the most universally banned, though sometimes muntjacs are permitted), though most states ban all cervids from moving into their state lines. Many states also require testing and permitting to even move deer within the state.
As you can imagine, all of these restrictions make it extremely difficult to manage deer programs, especially when these restrictions also pertains to simply transporting deer through states which inhibits zoos' abilities to transport animals between them for breeding. For example, I know the newest legislation passed in Louisiana has meant that the Audubon can no longer ship their Barasingha out of state, meaning the portion of the population kept between the zoo and breeding center are trapped there until further notice.
It's no surprise really that most zoos have simply given up on keeping exotic deer as a result of all this, as sad as that is. I know California and New York have particularly lax (and in my opinion very sound) regulations, both allowing animals planned for import to be tested immediately prior to transport as well as upon arrival in a quarantined setting, so this is why one will find the two major hubs of Asian deer in America to be the Bronx Zoo and the San Diego Zoo Safari Park. These two zoos almost single-handedly manage multiple Asian hoofstock populations between them, including the non-AZA North Indian Muntjac program. I know Bronx alone has roughly half the Barasingha in the United States.