All I can think of is that this is what was considered appropriate at the time. We have to take into account the philosophy of the Mysteries.

But note that Jesus is claimed to have said: “Nothing is covered up that will not be uncovered, and nothing secret that will not become known” (Matthew 10.26). See also Mark 4.22 and Luke 8.17.

Also Paul in 2 Corinthians 3.14-16: “to this very day, when they hear the reading of the old covenant, that same veil is still there, since only in Christ is is set aside. Indeed, to this very day whenever Moses is read, a veil lies over their minds; but when when one turns to the Lord, the veil is removed”.