The relevant difference here is that we have much more clarity around career-oriented programs and we're able to keep the slope under control. Most people can find and establish a reasonable career for themselves. We use a lot of economic tools to make it so it's possible to break into a trade or career, including university, etc., and these programs have been successful in keeping "the slope" semi-reasonable. This
has not happened with obesity. We've allowed the food conglomerates to run roughshod over American health in the name of greater sales.
(There is also the difference that it's a lot harder to justify extreme effort expenditure on the tasks necessary for daily biological maintenance, like eating.)
If something is impossibly hard for most people, the answer isn't to scream until the populace does the hard thing, the answer is to try to figure out a better path. You've surely heard the expression "work smarter, not harder".
Taken to its extreme, your logic disavows practically all tools of human invention. "Why would you expect to be able to dig a hole without weeks of labor, clawing away at the dirt? The ground didn't get there overnight and it's not going to go away overnight." We could use a manual shovel and reduce the effort investment by an order of magnitude, or a construction machine like a front shovel or auger and reduce the effort investment by (at least) another order of magnitude.
"Just try harder" is essentially just telling everyone else to claw at the dirt with their hands. There may be a handful of people with just the right combination of determination and imperviousness to self-harm to do this to get a hole, but the vast majority are going to give up early, and it's the same way with the obesity epidemic. It's not about "getting something else to do the work" (again, I think one of the root problems is our supply chain, something most Americans have little to no control over). It's simply about finding a solution that works for the 80%+ of American adults that don't get "the recommended amount" of daily exercise (to the extent which some of these people are non-obese, it's mostly a biological accident (one that is liable to break as they age)) and buy their food from the normal grocery store.
We need to see it as the macro problem it is instead of making a collective assault on the character of the people who can't do it. That may have been an OK solution for the first few years, but it should now be apparent that it simply doesn't work. The trend keeps getting worse. I understand it's hard to let go of that perspective since part of the appeal of fitness for many is the superiority complex, but it's not doing us any favors. We need to let it go and focus on finding a real solution, whether that's returning to a normal food supply, utilizing pharmaceuticals intelligently, redesigning our working lives to include more requisite and natural calorie-burning activity, or something else, we need to find an answer that works and stop clawing at the dirt.