Not Controlled Here, rather than Not Invented Here.
The GPS is not under the control of the civil aviation authorities, which may make them nervous about trusting it - especially when the entity in charge of the GPS has declared the ability and intention to degrade it regionally if it suits their requirements (the US DoD declared an intention not to use the global Selective Availability feature any more since they could degrade GPS regionally if they wished to).
One way to approach robust systems design is not to use anything you can't specify and control. VOR/DME, ILS, etc are under the control of a CAA, the GPS is not. I'm sure this mindset influences some certification requirements (in aviation and elsewhere). It is clearly a driving force behind GLONASS, Galileo and whatever the Chinese are working on (currently called Beidou I think).