1) There are very serious long term side effects, people are just either unaware or value weight loss enough to tolerate/accept the risks and harms.

2) Your "aside" there is the whole thing though. Obesity drives a lot of costs sure, but Obamacare legislation enshrined health insurance companies and pharmacy benefit managers as essentially government-backed money printing machines, so it's going to take tremendous effort to change any legislation, because they can and will spend literally billions of dollars to keep their monopolistic position.