It frustrates me when a zoo goes to the trouble and expense to import and them they phase them out more than likely as @Zoofan15 has pointed out yesterday because the number obtained was likely to small to start with!
It seems the issue of importing a small founder base is two-fold in that the numbers aren’t there to generate succession; and that the level of inbreeding then becomes a concern to the point breeding is ceased.
Prime examples of the latter are Collared peccary (descended from a single pair), which Melbourne have made the decision to no longer breed; and Rothschild’s giraffe and Grant’s zebra in the 2000’s, where hybridisation with generics was chosen in preference to inbreeding.