"How do you explain a lack of belief in the Real Presence by a majority of Catholics today?"
That is a somewhat controversial thing to say.
However, even if one were to grant it for the sake of argument, one would find that those who attend Mass on a weekly basis are far more likely to believe in the Real Presence than those who don't (and the absolutely stunningly overwhelming majority of Catholics who go to Mass on Sunday do so at a new Mass).
If the assertion is true, that participating in the new Mass causes people to lose belief in the Real Presence, then we would expect that those who are most exposed to the new Mass, i.e., those who attend at least every Sunday, would have lower levels of belief than those who are much less exposed to it, i.e., those who don't attend at least every Sunday.
One must be careful how one interprets causality when all that is really known is correlation.
sitetest
In fact, I've noticed that those who believe in the Real Presence most ardently in my own (Mass of Pope Paul VI) parish are those who attend most often.
Please reconcile this fact with your theory that the new Mass causes lack of belief in the Real Presence. ;-)
sitetest