I think the difference is that often, MO kids choose to get married later and are not part of the “shidduch” crisis. I also know that sometimes, formerly RW people become MO as they stay single. So they move from pot to pot.
What is this based upon? I happen to know many more people who’ve gone the other way, from MO to RW.
Just consider the fact that YU decided to invest 6 million dollars 4 years ago to address the “problem” of MO people going RW.