That's a good question.
An educated guess is that most of these "experimental" drugs finally make it into the insurance companies' roster of drugs they'll pay for. They delay as long as they can in order to save money without regard to lives. There is, of course, overseas sales and the very wealthy can afford the drugs. The drug companies who develop these expensive drugs would lobby the insurance companies to get their drugs listed on their rosters. I would imagine there is a lot of wheeling and dealing going on.