How and why did Family Matters go off the rails so badly?

For the first few seasons (more specifically, prior to Season 5), it was a universally relatable show about a working class black family. It was basically, like a more blue collar/working class version of The Cosby Show. And, then they turned the show into slapstick and an over the top sci-fi live-action cartoon when the Urkel character caught on.

Oddly, this whole dynamic of Family Matters seems like what happened to Good Times about a decade and a half prior. Esther Rolle and John Amos signed on to be in this quasi serious drama about black family in the ghetto. And then this comedian with a catch phrase (Jimmie Walker) becomes star of the show and now the show is about his antics and shenanigans.

And going back to Family Matters, eventually, the Winslow family and other characters just became props and took a backseat to Urkel or left the show all together. And eventually it wasn't even just focused on Steve Urkel anymore, it also became all about his alter ego Stefan. The bottom-line is that everything about the show (all the characters, storylines, and plots) became so tightly centered around his character.

Think about it this way, how do we go from talking about Mother Winslow's quilt and talking about gun violence in Chicago to Carl and Steve shrinking themselves and laying under a piece of cheese in a sandwich?