Stupid question, but why didn’t the DOD mandate IP compatibility for literally all comms like 20+ years ago? Is it pure corruption/incompetence or is there a good reason?
There's a very small number of major contractors and if you pick one of their APIs as the new standard, then you disadvantage all the others.
If you pick a greenfield project, then it will take a long time, and once you are done everybody will claim that they can't use it (see e.g. Ada; quick version they started working on a mandate for a programming language in 1975, mandated Ada in 1991 and by 1996 removed the Ada mandate).