What are you talking about? Building muscle is much easier than losing weight. You just have to lift heavy things on a regular basis, and eat something more nutritious than ramen. If you work out, the sleep takes care of itself. Losing weight, on the other hand, requires self control.
Yeah, no. Not by a million miles. Not eating is easy, you just ignore the hunger pain. Gaining weight is extremely hard for some people. I bet you don't know the feeling of forcing your 2nd dinner down your throat and trying not to vomit at 1am before going to bed because you're still 500kcals away from your daily caloric goal. Or setting an alarm every 90 minutes to eat yet another meal.
Millions of people having problem A doesn't make problem A harder to solve than problem B. I bet most overweight Americans don't want to lose weight. Of course they want to be at that ideal body type, but they don't want to put in the effort and changes to diet and lifestyle it takes to get there.
But we were talking about people actively trying to lose/gain weight, and willing to do the sacrifices, which is a different set of people.