I guess it's a goofy (and funny) depiction of a typical American family and people surrounding them. Like the other commentaires say, it's just a comedy and doesn't always have to make sense.. as long as it makes people laugh. Hope this réponses your question!!
I think the Simpsons are not only funny, they often have subliminal messages in the episodes. After watching some of them twice ou three times, I noticed some social and political criticism. Much of that can probably be only understood par US Americans and of course there are some episodes that are just for fun.