Nobody blocked the doors.
At the time that the Church had these prayers, the general mindset of the great majority of Catholics was obedience, and in many ways, was strongly towards, or approaching.blind obedience for many, if not most.
That was true also for the majority of the public. This was in the heydays before the revolt of the '60’s was in full swing.
Most people simply did not question whether or not they could leave; they just stayed. In fact, most people, if you asked, would probably have said that the prayers were part of the weekday Mass, as most people knew almost nothing of liturgical rules. It was what it was, and no one questioned it.