Why do some people want to gain weight?

There is a such thing as being underweight, just as there is such a thing as being overweight. It is not entirely about looks- it is a matter of health. Some people want to gain weight to reach a healthy weight, while some want to lose weight to reach a healthy weight.
It's about that balance. You don't want to eat so much unhealthy food that your body reflects the unhealthy habits- and you also do not want to eat so little that your body reflects the same. Though bodies are also just built different- some people are naturally a bit curvier or heavier, or have a faster metabolism that keeps them slim. So weight does not always reflect nutritional habits, but most often does. It is always a good idea to do what you can to maintain a healthy weight, be that by gaining or losing weight.

The same reason people think they should lose weight, even when not overweight, there's people who feel the same about being too skinny. It's a struggle that people deal with and even though I'm trying to lose weight i feel horrible for those trying to gain as well even though it seems easier to deal with, it's not

🤷🏻‍♀️ I intentionally put on weight because even though my bone structure has hips no matter how skinny I get, I disliked the xylophone torso look on me

I am 187 3/4 pounds but I round it up to 188.