And they were packed even when Mass was typically the Low Mass (which was supposed to be for priests' private Masses), and badly said, at that.

That's a point in favor of God-centered, reverent liturgy in which the action expressed the truth: even the most unsuited version, done shabbily (a sin!) was treated as though important.  God was in His place and Man his and the priest constantly reminded (in the prayers) of his own unworthiness.

The Mass as the "closed circle", horizontalized, celebrating the gathered congregants (some theologians "of a certain age" even muddling the congregation and the Eucharist) is a formula for disbelief in God.  If that's what we offer the youth then the youth are right for rejecting it as it celebrates a false god.  

This near-idolatry isn't what we are required to offer, and there's nothing about the Ordinary Form of the Mass that requires it to be celebrated horizontally.  But it (horizontal Mass) is the Sunday experience of the last 2 generations.