And the food industry definitely needs to change to make it easier for people to affect their slope.
And regardless of all of that, I would rather tell people that this is hard and that it requires a lot of work and effort on their part, than to encourage them to give up after quickfix solutions don't work.
Ultimately it's about patience. If you do something, anything, every day (even going for a 10 minute walk is better than nothing). And if you are even remotely careful about what you eat, you will see results. Maybe not today. Maybe not tomorrow. But if you keep it up for a few years, results will appear out of nowhere. And this stuff gives you compounding returns. The longer you do it, the quicker the returns on any new thing that you try.
When it comes to people you love, would you rather tell them that they are helpless victims, or that they can overcome their problems?
Here's a question for you: if we agree that being good at your career takes daily effort and practice for the majority of life, why does this conviction fall apart when it comes to diet and exercise? Why do we assume someone else should take care of that, not us? That it should somehow come as if by magic? It's a skill. You have to practice it to get better.
(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.
This is how I put diet and exercise into perspective now. If I told someone I wanted to learn how to paint or play guitar and I started complaining in 2-3 weeks about how I'm seeing no progress, they would immediately be able to see how unrealistic I was with my initial expectations. Diet and exercise are no different.
I believe it is sufficiently proven that it's not that people don't want to be at healthy weights (barring a handful of online extremists), it's that "the slope", as you refer to it here, is prohibitively difficult for the vast majority of people to overcome. That difficulty has to be broken down (and I personally believe fixing the issues in our food supply is a very important part of that -- it's almost impossible to buy healthy food in the US without going to a specialty grocer, no matter how hard you try). There are many ways to approach the problem, but right now the primary effort seems to be on just yelling at people to try harder. That works in some cases, but not nearly enough to be the only solution we have.
The discord on this topic originates from perspectives like this, where someone takes their personal experience and extrapolates it onto the rest of the population. It's great that you got fit, and it's great to encourage others to get fit too. It's not great to trivialize the complexity of the realities that contribute to the obesity epidemic. "Everyone else is a just a fat, lazy glutton", the crux of the fitness camp's argument, is popular because it's self-flattering and an effective marketing technique, but it's an extremely naive and superficial perspective on a global health epidemic, and it isn't going to motivate a great deal of progress on the issue.