Looks like it was a student project if I'm reading it correctly? So nothing official from the zoo, much like the old plans that I remember being shared here that intended to put manatees in The Clore. Regardless, I suspect money and the want to maintain the aviaries that were then there would probably have been the main contributing factors. Certainly money is the main reason it's empty now

The current leadership is doing as far as I'm concerned an exemplary job of managing ZSL and maintaining financial stability, but hopefully once the major infrastructure projects are done the North Bank will finally see some love again.
Personally, the dream would be a dedicated pangolin house.