The reason they don’t allow repair as such is twofold: competence and liability. Both increase the risk of the equipment malfunctioning in the field. This leads to dead people fairly quickly.
Repair is one of those things where the Dunning–Kruger effect is very real.
Source: the guy who used to work at the contractor doing the repair or disposal evaluation of things which had been attempted to be repaired.
The underlying issues are far more nuanced than that. In fact, it has little (if any) to do with manual labor competence and/or liability risk; if you can be trained then you can be summarily replaced, and the risk is hardly a support contractor's prerogative to assume.
The root cause of these issues (as I see it) is almost entirely traceable to tech data availability/quality, commercial influence on DFARS data rights language, and the acquisition games being played (of which the general public only every catches superficial wind surrounding ACAT I programs).
Repair is one of those things where the Dunning–Kruger effect is very real.
Source: the guy who used to work at the contractor doing the repair or disposal evaluation of things which had been attempted to be repaired.