Maybe the driver didn't want to risk getting a parking ticket?
Last time I passed the zoo, there was no legal parking/drop-off at the front. And around the back, technically it's "buses only." So the taxi driver would have to go into the public car park and hope for 2 adjacent empty spaces (can't use the disabled bays without a blue badge) or
drive up the North Road (one way now!) at the back of the Zoo and drop them off there and let them trek back to the zoo entrance!
The zoo is not very taxi friendly

Used to be a handy spot to swing by if you were nearby because parents and tourists would be knackered after traipsing around the zoo for 3 hours and they'd be desperate for a taxi back into town. But not anymore. There's nowhere to stop legally.
/rant
