Years after Fuller House ended, Mary-Kate and Ashley Olsen debunk the biggest rumor about why they didn't return in the Full House spin-off. The twins alternated played Michelle, Danny Tanner's youngest daughter for eight seasons of the original series. However, while the rest of Full House's main cast came back to Netflix, they didn't. There were claims that it was the biggest they didn't have as much fun doing the original show as their former co-stars.
https://screenrant.com/fuller-house-olsen-twins-never-return-rumor-debunk/