The excuse they'll give you: the responses of "Lord have mercy, Christ have mercy, Lord have mercy" adequately express penitence and therefore the Confiteor is unnecessary.
And instead of the Preface, I should have said the Sanctus. Perhaps both.
Eeek.
I wonder just how many people who attend Mass, where this is (sometimes unknowingly) omitted, think that:
(in my own short form) "I confess that I have sinned exceedingly in thought, word and deed through my fault...ect...and ask the Saints to pray for me"...
Is really "old fashioned?"
Nice "assumption" on the liturgical directors part, doncha think?
Wow.