Why is sabrina the teenage witch movie 1996 different?

I was just watching the sabrina the teenage witch movie were she goes to a dance with some jock. But as I was watching they were all different actors except melissa joan hart. Hilda and Zelda also Harvey were played by different people. But when you look up the cast it's the people that played in the later seasons. Even Salom sounded different. They didn't even live in that one house. It was all different the whole movie was different. The only thing that was the same was melissa joan hart playing sabrina.