To put it even more dramatically, even the 20 million who attended the JW memorial are more active than the inactive "members" of the Mormon church, the majority of whom never attend a Mormon church at all.
The Mormon church counts every single person who has ever been baptised as a member of the church, regardless of whether they attend or whether they still believe in the church. Mormons can only be removed from the membership total if they write a letter to the church renouncing membership, which relatively few ever do. If you stop attending church they still count you. If you attend a different church they still count you. If you move and they lose touch with you they still count you. They still count you until you are 115. Only then are you removed from the membership total and presumed likely dead.