Name changed for this. Not ashamed of having used WLIs by any means, but...
I was prescribed a WLI (not Mounjaro, this was pre-Mounjaro times) as a trial patient for T2 Diabetes. I was also clinically obese at the time. Over the course of 4 months, I lost 3 stone, with a further stone over the following 6 weeks or so,
I stopped taking it when the trial ended after 6 months. It took a few weeks for my stomach to get used to once again accepting all the food I had a renewed appetite for, and whilst initially, my calorific intake was still nowhere near as great as on pre-WLI days, I was still consuming far more than I had during the preceding 6 months.
Within a year, I had put back on just about every single stone and pound I had lost on the WLIs. And within another 6 months, an extra stone on top.
Why? Because the WLI did not regulate what I was eating, it didn't make me suddenly eat healthy choice foods, and it didn't miraculously embark me on a fitness campaign. It made me feel so crap that some days I had to almost pass out and force myself to even drink. I would frequently go 48 hours without any food whatsoever, and I'm pretty sure I would have been in a calorie deficit on more days than not. Is it surprising that the weight fell off me, and is it even more surprising that as soon as I started to eat even 'sensibly', the weight came back? My body was essentially in starvation mode a lot of the time, and as soon as normal eating was resumed, I guess it hung on to every morsel.
So yes...that's my explanation for why so many of us end up even bigger in the long term. It's not a miracle drug. It's a drug that often literally stops you from eating. In my case, it was pretty much like having a 24-hour stomach bug, 7 days a week. My skin suffered, my energy suffered, and my immune system was shot. I looked 10 years older and felt 30 years older.
Two years on, and a lifelong membership to WW, and I'm getting there again. It's taking a long time, but I've learned these things can't be rushed!