An improperly devised system that can be easily circumvented.
It is not relevant to the subject matter of health care, it is not different than corn subsidy or whatever.
But instead of doing that, they realized that they could just pressure providers to up-code and goose the risk score and make more money.
MA is relatively new. We needed many years of experience to see how the market would play out. But now we've known for a decade or so that it is clearly costing way more than it should and offering no additional benefits to justify the cost. Unfortunately we have not yet had the political will to fix it, and the handful of massive companies making bank on it will fight tooth and nail to keep the gravy train rolling.
The lesson from MA is that people will figure out how to game the rules, so we need to be reactive and flexible and able to update the rules accordingly. But because health care is a complicated and personal subject, people are wary of change, and we have very little political will to fix this. This will get even harder with the recent Chevron decision, which will serve to make it even harder for CMS to fix the regulation of MA without new legislation.
I'll simplify it for you: The government pays health care providers for providing healthcare. It is very easy to defraud the government by billing for fake work, so fraud is common and costly.
The actual details are irrelevant. There are some extra steps involved, but functionally it's the same as a nurse sending a bill that says "I treated patient X for condition Y" and the government going "Sounds good, here's some taxpayer money"