I know a number of opinions (but with no backing data) have been put forward, mostly alleging higher traffic density, but even if that is the case, surely you would then go and hire more controllers to deal with that? I struggle to believe that such a comparatively expensive place to fly can have such an appalling level of service.
I'm sure you know the answer to that one really:
"Hiring more controllers costs money. Who is going to want to pay them? - not the GA pilots wanting transits, and why should anyone else?"