...once upon a time. Still big (for now)...but not the juggernaut it once was.
I attribute part of this to the fact that Catholicism has lost a lot of adherents and influence. The "Subway Alums" were primarily working Roman Catholics that adopted ND as their own. The woes of the Church and the general waning of religion in America have been a detriment to the scope of ND's fanbase.
Additionally, the "average Joe", whose kid excelled in high school, can't get that kid into ND anymore as a rule, unless the kid is an absurd brainiac. I think these things are parts of the equation that factor into the declining numbers for the overall broader appeal of ND.
People revere the academic excellence still and once respected that they promoted education (even for top athletes), but competing at the highest level in the "system" now negates holding the top recruits/transfers to high educational standards. The rose has lost some of its bloom...if you will...sadly.