They do it for one reason: Because they can. The majority of MC owners paid outrageously high prices to buy their units, and want to believe that it was worth it, based on distorted views of the cost of hotel rooms in Manhattan. Also, they are still trying to sell what is now a lie: "We are the only timeshare in Manhattan." So, the management knows that it can further rip off the owners by charging outrageously high annual fees for the same reason. Notice that the fees are not being used to maintain the property -- it is deteriorating quickly, was shabby eight years ago and is going downhill even more quickly now.
The one thing left about the MC that is good is its location, but with the cropping up of multiple other timeshares in Manhattan, there really are much better choices.