GLP-1 is produced by the body to regulate and balance food consumption. People whose bodies produce less than the correct amount eat more because they feel a lot more hunger than people whose bodies are normal. Taking in GLP-1 drugs, if following medical advice, brings their level back to what it should have been all along, in which case most wouldn't have become obese at all.
I'm such a case. Clinical exames never showed up any clear problem associated with weight gain, so for my entire life my obesity was linked by everyone, doctors included, to lack of willpower.
I only discovered what my issue was when I took a genetic test and discovered that my DNA came with these lovely traits:
* I feel more intense hunger than the average people, so I need to eat more than they do to feel satiated. If I eat the same amount a normal person does, I leave the table literally still hungry.
* My body accumulates more fat than the average person, so even if I eat the same amount they do and keep constantly hungry, I accumulate some fat.
* Caloric-reduction diets don't work for me. So the years and years I tried and tried them had little effect, and were mostly wasted effort.
* Fat-reduction diets also don't work for me. Good thing I didn't lose time with those since everyone recommended me the useless caloric-reduction ones.
* The only diet that has some effect for me is the Mediterranean one, which I didn't know about and no one had ever recommended.
* Physical exercise has little effect for me, as I gain less muscle mass from it than the average person. So the years of walking and the many attempts at going to the gym were also mostly wasted effort.
* And physical exercise causes more pain for me than it does for the average person, so all the time I was doing those, I was suffering more than most people while getting worse results then they do from it.
If your genetics is normal on all those fronts, then sure, a bit of willpower fixes that. With that combo though, and fully not knowing you have any of that? Not a chance.