OF₆ does not form, but SF₆ does because oxygen cannot exhibit an expanded octet, while sulfur can.

OF₆ does not form, but SF₆ does because oxygen has a much larger atomic radius than sulfur.

OF₆ does not form, but SF₆ does because oxygen is not electronegative enough to accommodate the bonds formed.

OF₆ does not form, but SF₆ does because fluorine can only form bonds with larger atoms like sulfur.