Training and education received in the Marines are usable later in life. Cults do not necessarily train a person in anything that has any value in the greater society. In the USMC, public records are kept and are available. Cult records, if they exist, are confidential, hidden from members, and not shared. USMC Inspector General procedures protect each Marine.
Nothing protects cult members.
In cults, there is only the closed, internal system of justice, and no appeal, no recourse to outside support. Families of military personnel talk and deal directly with schools. Children may attend public or private schools. In cults, children, child rearing, and education are often controlled by the whims and idiosyncracies of the cult leader. The USMC is not a sovereign entity above the laws of the land.