This is a statistical fallacy where you're only identifying the extreme cases. The average obese person loses 14-20% of body weight. (Remember that the "obese" category is already defined as 20%+ above the high end of the "normal" range.) So the vast majority of people on these drugs just look normal, not skinny or gaunt.
> They also complain of constant nausea and eat like a bird because eating makes them sick
This is a high dose phenomenon. They can and should reduce their dose if it is preventing them from eating enough or being comfortable.
> I worry about ... medical professionals not using it as a brief intervention then steering towards lifestyle changes.
They absolutely do, of course.
So people who were fat and get to a normal weight, if you've always known them as fat then they look like they've aged a decade or two in a year. People who were totally normal weight (i.e. "overweight" according to BMI, which is associated with a longer lifespan than "healthy weight") end up looking like tuberculosis Romantics because they wanted to look like movie stars (who are often on severe, unhealthy diets that they stop when they're not working.)
Losing weight quickly often loses it badly - think meth addicts. Women lose fat from their breasts and both sexes lose the fat pad around the eyes; I think these are generally stable fat stores that don't really replenish after being used, even if you gain the weight back. It's not specific to GLPs, just quick weight loss. If you'd lost more slowly your body wouldn't have resorted to taking from those places. Now, you have super-deep nasolabial folds and marionette lines.
> lost weight with diet and exercise
You lose weight through diet. You gain fitness through exercise.
I truly, truly do not understand where this mentality that the medical professionals don't encourage lifestyle changes comes from. If you smoke, they will hound you to stop smoking at every single appointment, regardless of what the appointment is for. They will tell you what to eat. They will tell you to eat less red meat, eat less processed food. They will tell you that you need to exercise 30 minutes a day. They tell you all of this, constantly.
That doesn't mean it works, though. You can tell someone to eat less over and over and that doesn't just magically make them eat less.
This is why anecdotal evidence is pretty bad.