Remember on the early enrollees who are signing papers. They are signing an aid package not a LOI. Alls it does is obligates the school to provide a scholarship but it does not commit the player to the school. Basically the school can no longer back out of their offer but the player can still go wherever they choose without penalty until they attend an actual class. They will still have to sign a LOI(even though a player technically never has to sign one).
Players that are early enrollees that haven't committed yet may sign grant in aid papers with multiple schools right now so the paper work for enrolling is done. Then when they commit to a school all of the enrollment stuff is in place. A school that a player doesn't commit to can just scrap the paperwork.
It is becoming a more common thing all the time. This way the schools cannot pull an early enrollees scholarship before they sign a LOI, but the player isn't bound by the signing till they sign a LOI.