I really don't want to come across as niggardly, but both Blackbuck and Nilgai are species held at Whipsnade in the very recent past that have been allowed to dwindle away through lack of interest. If you're prepared to go back twenty or so years, the same applies to the apparently impending Thomson's Gazelle.
Blesbok and Impala are also species held in the past, in an era when Whipsnade -again- was starved of capital so that big vanity projects could proceed at London. Thus African antelope at Whipsnade had to cope with shelters that were identical to those for the likes of Bactrian Camels and Yak. Unsurprisingly, they failed to thrive.
ajmc, how many other zoos have you visited? I'd suggest two, both vwery instructive in their different ways. Shaldon Wildlife Trust in Devon is tiny, and accordingly has had to keep smaller species. It still manages to keep eighteen species of primate, Margay and Owston's Palm Civet. I think its director would give his eye teeth for some of the land left untouched at Whipsnade.
Whipsnade is not a zoo standing on its own; it is part of a community of European zoos, all committed to the care of endangered species. A zoo that leaves that amount of space untenanted is, quite simply, letting others down.
East Berlin, on the other hand, is huge. I am not an enthusiast for much of its carnivore collection's housing, but its ungulates are a joy. Kiang; Bactrian and White-lipped Deer; three forms of Takin; Marco Polo's Sheep; Bharal and Markhor are all kept, amongst many others. All are temperate zone species which would cost a pittance to stable and all would benefit from extra holders within EAZA.
As for ; well, Whipsnade is competing (and against tough local competition in the shape of Woburn) for the hard earned money of ordinary people. The standard two child family would pay £81 to get into the park, without a car.
They deserve a few more filled paddocks for that!