Well, let’s see…
The people, in general, were not participating in the Mass, but were praying independently and merely Witnessing the mass, or even merely being present but completely isolated intellectually from it. (I remember in my childhood, a priest asked someone to stop praying the rosary during the readings and the homily, as it was disrupting others ability to hear the teachings.)
The primary reason for this disconnect was, according to the V II post-conciliar documents, presumed to be the lack of comprehension of both what participation is and what the prayers mean.