Just off the top of my head the food (portions, quality, etc) in the USA combined with how much people no longer can walk vs being required to drive are a huge contributor to weight gain of immigrants to the USA.
There are of course other decisions that might help cope, like moving to one of the few walkable cities we have or structuring your life to reduce the lifestyle, but those all have a lot of other effects like completely upending your current life.
What’s a person supposed to do about a problem that’s probably tangled up in several major areas and would require large reforms across the economy? We can’t even get mandatory minimum paid leave or healthcare for everyone (both of which might well be components of fixing it “right” anyway!)
This is likely a problem that spans our food culture, business culture, economic structure, built geography, and social benefits system, among other things.
You can spend a lifetime fighting those and be fat the whole time because despite massive effort and objectively incredible achievements you and your movement only got us 5% (that’s a lot!) down the road towards fixing these things, in fifty years.
Or you can take a weekly shot and be well on your way in a month.
Working on the “real” fix is definitely something we should do (it’s not like the causes of this aren’t causing other things to suck, too) but even people doing that would probably like something available that they, not just their great-grandchildren, can have.
Well-studied problem.
It makes more sense when you realize that something like sheer dieting/exercising willpower isn't why some populations are skinnier than others. Pick another country with a healthier-weight population, start placing some of them in the US, and they'll gain weight. Put them back, and it'll drop again.
If "just diet and exercise" (the advice, and individual effort to that effect) aren't what are keeping some populations skinnier, why would it cure a population with an obesity epidemic?