One way to think about all of this is in terms of costs and benefits.
The social and economic (and possibly health, depending on your read of the literature) benefits of being thin, and of losing weight if you're fat, are high, so most people will try to get and stay thin.
Until recently, it's been extremely costly to get and stay thin if you're fat. Costly in terms of dollars, but also time and effort. "Diets don't work": most people have to work hard against ingrained biological mechanisms that hold onto fat. The exceptions were either too difficult or costly for most people to access (WLS, for instance) or otherwise too dangerous to people's health (e.g., becoming a drug addict).
GLP-1 inhibitors change the game by making it much less costly to get thin and stay thin. More so than ever, it takes less money/time/effort to get/stay thin than in human history. It's still too soon to reliably measure the exact magnitude of this effect, but it's reasonable to expect that this has at least slowed, if not reversed, the rate at which the population has gotten fatter. But, even so, the costs aren't zero: the medications remain expensive, insurance coverage is limited, a not-small minority of people get prohibitive side effects, etc.
So if the goal is to keep that trend line going up, you can either raise the costs of thinness, or reduce the benefits of thinness.
Body positivity and fat liberation have been trying to work on the latter. That's an uphill battle, to say the least, but because the costs of getting/staying thin were still pretty high in the 2010s, some small headway was made (and a big backlash initiated, too). BP/FA folks could make the pitch, "if keeping off a bunch of weight is really out of reach for most people, perhaps consider rethinking body size?" But since the costs have fallen in the past few years, it's put those movements on the back foot.
On the costs front, pharmaceutical companies and medical institutions are trying to reduce costs further: developing medications with fewer side effects, developing pills instead of injectables, expanding insurance coverage, etc. TBD how much headway any of those efforts makes. The highest "cost hike" would probably be finding out about more severe medium-to-long-term effects of using these medications, but I don't think anyone can count on that, nor do I really want to (given how many people are on these drugs already!).
So yeah, that's how I think about it: people will keep getting fatter if it becomes more "costly" or less beneficial to get/stay thin. Achieving either in an ethical way seems very hard at this point!