Sorry but why must all hip hop be about serious issues or violence?

I don't like Soulja Boy but i really like Lil' Mama! I like the fact that Lil' Mama has an equal balance of funs songs (Lip Gloss, Shawty Get Loose, G Slide) and more serious stuff (L.I.F.E, College etc) Hip hop doesn't all have to be about the seriousness of life!