This is easy.
1. Look at the longevity of it's success not only as a black sitcom but a sitcom in general
2. It was the main catapult to its "TGIF" comedy line up on ABC
3. The character "Urkel" was widely recognized no matter how you felt about the character.
4. It touched on a wide range of topics
And 5....most important...it showed a chill, successful black family on tv and it never used any over the top black family stereotypes to depict their family...