@lintworm summed the situation up pretty much perfectly some years ago:
Money is not a problem here and they will fly in constructors from all over the world and ship in original building materials and art to give an authentic experience. This is probably the only zoo where Orangutans sh*t on real marble........the rate at which this zoo is being developed is staggering, but cannot keep up with the speed at which new, and often rare, mammals are brought in. So new species are often first kept in inadequate enclosures until space is found.
I would argue that - despite the footprint of the zoo having expanded significantly since he originally wrote the above words, and therefore a larger amount of space being (theoretically) available - the situation has not improved; the bad bits remain as bad as ever, both in terms of sub-standard enclosures and tacky, sometimes viscerally-repulsive theming.