What?
Who laughed at them?
Well not everybody, but G-Unit with all their pop fads like hand gestures and clothing lines, and Dipset with their similar shit like with throwing the eagle sign, was sort of silly. Maybe not if you're used to killing people after throwing a gang sign, but most people probably thought it was stupid. Thus, the groups are associated with that stupidity and people jump on band-wagons instead of judging the music.
Regardless of what I think about some of Dipset's music, which I like, I also know that whenever I see some wigger boy dancing in a club he's normally dancing to G-Unit, Snoop, Pharell, Dipset, Young Jeezy, Lil Wayne, Souljah Boy, your typical pop fad artist who does more than just make music.
I think there's several explanations. One is that group acts have been around for a while, and we know there's usually internal conflicts and shit. Nobody wants that shit, so going solo is just easier, which is why I think a lot of people just do that without even considering anything else.
Take myself for example. If I were to ever become some superstar, I want to be the most super there is, not share the throne with some other dude. I want to be king, and if not I am content where I'm already at.