Many airports have been charging for trolleys for 20 years or more. The cost of managing them is enormous and the only problem can be not having local coins when you arrive.
I have just come back through JNB and they do not charge which surprises me. Firstly because of having the very smart trolleys that are strong and designed to go up escalators (brilliant) and because the rate at which they disappear must be very high.
Actually, come to think about it, the trolleys were the best thing about the airport.