Why does the priest not face the people in the celebration of the Extraordinary Form?
Because he is offering the Mass in Christ’s name and in His Person, in persona Christi, to God the Father and is leading his people in adoration and worship. He is facing east, the rising sun, which is symbolic of the ‘New Jerusalem’ and he is leading his flock as the Good Shepherd does. When he needs to address the congregation he turns to face the people and says, for example, “Dominus vobiscum” (“The Lord be with you”) or “Orate fratres” (“Pray, brethren”).