While obesity is a problem and the solutions heavily involve the person changing their life, it is not comparable to vaccines.
Fixing obesity involves education (not everyone knows why McDonalds is junk, or that too much of anything can be bad, meaning portion control), skills training/learning (cooking healthy food can be a big leap for someone who only microwaves a frozen meal), local environment (there are places with poor selection of fresh vegetables), lifestyle stuff beyond food (stress from working two jobs leads to eating badly, drinking, etc), and socioeconomic changes (not everyone can afford all of the above easily). That doesn't even involve things like getting you kids on board, fitness, etc.
And with all of that in place, significant weight loss is a long term effort spamming years for some people.
Getting a vaccine involves rolling up a sleeve then sitting for a bit in case of reactions. And maybe making an appointment.
Equating the two grossly overstates how hard it can be to deal with obesity vs getting a shot.