As for MO, until about a generation ago it was a diving board from which the sons and daughters of its stalwart members, especially those who wanted to enter the pulpit rabbinate, jumped down to the conman movement and even lower. Its members were similar to those who call themselves traditional in EY – baseline kashrus, shul in the morning, shopping in the afternoon.
Then, when the going became a bit easier for shomrei Shabbos in the workplace after the civil rights movement and, more importantly, when the Torah-true world was more firmly established in the 60s and 70s, MO had already dropped its “shvachers.” The remaining MO, who were more Torah-committed but tended to be of second-or-third generation American stock rather than immigrants and first-generation Americans like those who rebuilt yeshivos and Chassidus, began to move to the right. They started to look to the rabbonim and even the Rebbeim from Europe for leadership, as they realized their rabbonim lacked in scholarship and did not represent Torah values.
Now, it is only a matter of time before the right wing of MO (most of those who are committed to MO), most of the yeshiva world, and Chassidim who want to enter the modern world mostly to be able to raise families with dignity, converge. Gone will be welfare dependency on the one hand, but more important, “Torah uMada” will be buried with dignity, in favor of intensive Torah learning combined with secular studies for parnosso only. Even 25 years ago, I knew of no serious YU student who wasted his life studying philosophy or anthropology – most leveraged their year in EY to finish YU in three years or transfer to Columbia engineering school before going on for a law degree or MBA.
Left out will be the left wing MO, who will jump down to YCT (a malignancy that cannot last but a generation) and then to “renewal” or who knows what, and those who choose or are socially pressured to choose an isolationist way of life. The former will sadly join the secular Jewish malaise, and the latter will find it difficult to cope and eventually become a small minority.
Regardless of the above, the dropout rate among people who truly follow MO, as opposed to those who just go to MO shuls, cannot be 50%. Calling the crowd that was never observant “MO” is like calling the Israelis who come every Shabbos to eat at a Chabad House in Thailand or India “Lubavitchers.” It indeed WAS about 50% in the 50s and early 60s.