Some go outside of the box and are actually funny and original. As to why this format is still around... it's funny to most and it's familiar too. Ever been scared or grossed out by something on TV? If yes, you'd probably find comfort in quickly turning to a sitcom that has a familiar formula and will most likely not scare or gross you out.

The good ones are very amusing and that is why we watch them. The biggest problem is that when one is different and very good, then other networks try to copy it in some way with the result that people who only see any of them later, may not realize that one was novel until the others were "created".

Theyre fun

They're funny

Sitcoms are some of the dumbest shows ever to come out of America (though reality TV shows are even dumber), and they always do the exact same thing. Also, they propagate outdated stereotypes across the board, and they always end with the same message. I have two questions: how are they so common, and how has their popularity endured?