I guess the changes we see in the masterplans are for the most part reflective of the dynamic nature of the zoo industry.
In the past decade, sun bears have became a species that the region has identified for phase out (based on multiple justifiable reasons); and it’s no longer perceived as ethical to hold elephants in city zoos.
As an example of this, Taronga mentioned plans to build an elephant trail traversing their zoo close to a decade ago in their masterplan. I suspected they put this near the end to give them time to assess the current mood - and consequently in this time, decided to discontinue with elephants (in line with Melbourne, Auckland and Perth).