The international conventions are just another revenue generation scheme for the Org. They make money on the grossly inflated hotel costs , transport , kick backs from the host cities ( sometimes pretty crappy ones that don't get a lot of tourist trade. ) etc etc.
The host cities don't seem to understand that most JWs ( even the wealthier ones that go on such trips ) are quite cheap - they aren't always going to be spending $xx in restaurants etc - so the usual subsidies and formulas based on "we are bringing X,000 "delegates" to your city , pay us $X per head" don't apply.
A relative of mine went to Canada for an international assembly a couple of years ago but he returned somewhat unimpressed. He only got to see one or two of the popular tourist spots - most of the time he was doing JW stuff. There were a lot of requirements and restrictions - even down to having to wear meeting attire a lot of the time ( including on the flights. ) The hotel cost 40% more than it should have done ( and he didn't even get any reward points. ) He even had to go out of the ministry one day ( his wife feigned sickness & spent the day seeing some of the tourist sites ) !