Other mistake: Eddie drives the car through the front door. This shouldn't be possible. Whenever the front of the house is shown, we see that the porch is several feet above the ground and the only way to get to it are steps that aren't wide enough apart for a car to drive between them.
Other mistake: When Eddie and Carl are out ice fishing, you can tell the background is just a wall. If you look towards the bottom, you can see the line all the way across that would make it look like a wall of scenery.
Other mistake: Even though this is the first time that the kids are being introduced to the "Urkel Dance," Maxine is mouthing the words to the song as she dances.
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.