Why is it easier to believe that Facebook would want to ask for a user’s phone number twice: one for 2 factor verification purposes and one for notification pur

Why is it easier to believe that Facebook would want to ask for a user’s phone number twice: one for 2 factor verification purposes and one for notification purposes, rather than storing it just once? Given it was obvious they would get crucified by folks for spamming a 2FA number, why do you believe Alex Stamos and Facebook (a public company with React, Jester, etc.) are now lying to the public rather than this being an actual bug?