Why are 2 of the main characters not in the later seasons?

Does anyone know why>!Stacie and Danny!< are not in Season 5-8? I’ve been watching from the beginning and imagine my surprise when my two favorite characters didn’t appear 🥺😭

I only watched one episode of Season 5 so far and don’t know if it’s worth it for me to continue. The show is just not the same without>!Stacie and Danny!< imo.