Perhaps different contracts outside the US? I recall that this was contractual. In exchange for a lower plane price US DOD agreed to outsource maintenance to Lockheed. I do not know the details but was shocked.
Note the graphic says "Lack of access to technical data" That is similar to what I read a while back. Lack of parts depots is what Dreizin highlighted.
Kinda like promising to only have car repairs done at the dealer.