Maybe JP can correct me if I am wrong, but...
It's because the American Osteopathic Association in those five states are very strong...so they try to force everyone to do an AOA residency or a rotating internship year that is AOA related.
So, if you go ACGME without getting resoultion 42, they'll try to revoke your ability to come back and hold any sort of teaching position in any AMA or AOA school if you do decide to go down an academic route after you graduate.
This means you'll never be a program director or teacher at any LCME or AOA school in Pennsylvannia, Michigan, Ohio, Florida, and West Virginia. The osteopathic schools in these states have a lot of power over their state liscening organizations. Suprisingly, New Jersey isn't one of those states despite having many practicing DOs and its own public osteopathic school.
You can still go to an ACGME residency and say, "Heck with the AOA, I ain't gonna teach at any medical school ever" and you can still practice fine...but you never know cause one day you might have the opportunity to become a program director or try to get a teaching position at an MD or DO medical program...and the AOA is going to say, "Wait a second, you're a traitor to our cause!"
For example, I go to WVSOM. At year four, let's say I decide to do an ACGME residency at WVU and bypass the traditional rotating internship year. I also decide to choose an ACGME residency over an AOA one in West Virginia...
...What will happen to me? Nothing. I can go to WVU, Duke, Case Western, Mayo Clinic, and become whatever I want. But what if I decide I want to go back to WVSOM and want to become a teacher there? Now the AOA board has the power to prevent me from becoming a teacher there. What if I try to become one of the school's staff physicians at the Lewisburg health clinic? Nope. I can't do it. And they would rather hire an MD over a DO who did not do an AOA residency or AOA rotating internship. Trust me, it has happened twice so far.
If I turn against the AOA in those five states, I will be forever exiled to the allopathic world of medicine in those five states.
I know...politics is complicated....