>For a while he tried to explain it all by his weight loss alone, but over time he realized it was an overall change in everything about the way he carried himself and presented himself to the world.

All of what you're saying is just looks. Clothes, posture, etc. all matter and we all know some exceptions to the rule, but people make clothes look good and not so much the other way around.

>Now that GLP-1s are everywhere I do know a few people who slimmed down rapidly without changing anything else and expected things like their dating life to completely change but have been disappointed that little has changed socially for them.

Not everyone looks better if they slim down. And if you do it the wrong way, or don't update your clothes to not be baggy, or just plain have excessive expectations, it's going to be disappointing. Losing weight just gets you to the baseline of where you might not make people want to look away or find reasons to not like you. If you're short, then you'll still be short after losing weight. If you're ugly in the face, you'll still be ugly, if not more ugly. I know you're talking about men because even overweight women have lots of options. Dating is also nearly impossible for average men now. You shouldn't assume that weight doesn't make a huge difference based on a few examples of guys who can't get dates. Think of it more like not being fat is to make others not immediately blow you off for that one reason.