Continuity mistake: From the outside of the house, you can see the staircase and door are to the far left of the house. But from inside the house, you have a fireplace and the staircase to the right of the door. So you know it's not the same house they use in the show.
Continuity mistake: Whenever the characters in this sitcom fall through the roof, they end up on the living room floor. The house is a very conventional design with a second floor and an attic, so they should end up in the attic or on the second floor.
Continuity mistake: The Winslows' front porch as seen from inside their house features a lattice wall with vines and furniture. However, establishing shots of the house show no such features.
Answer: It is said that as Steve Urkel became a more popular character on the show, Judy became less important to the storylines, plus either her or her parents were demanding more money, causing her to be removed from the show entirely.