You’re pretty angry for someone who has limited knowledge on this topic!
It’s highly subsidized by the gov’t so the fee is trivial compared to the benefit. 2019 budget is $99B. Monthly cost is a little over $200 if you pay full freight.
Unless you’ve got other insurance, you’d be stupid not to go with Part D. You’d pay more with a private plan.
Medicare Part D plans (private insurers) compete for customers and get money from CMS for offering coverage that confirms to CMS standards.
It’s far more than “negotiating block and cost averaging”.