No oral modification clauses, part IV

In responding to an earlier post on no-oral-modification clauses, in which I questioned why NOM clauses were strictly enforceable in government contracts but not in private contracts, reader John Patrick Hunt wrote:

Wouldn’t the often-asserted superior efficiency of private enterprise suggest better supervision of agents and thus less need for a bright-line rule enforcing NOM clauses?

I’m not sure why this would be so, even assuming that government agents are less reliable than those of private parties.  The NOM clause is one of the things that private parties put into contracts to supervise their agents.  Maybe I’m missing something (it’s happened before), but taking away one of the tools private parties use to supervise their agents on the grounds that private parties do a better job of supervising their agents seems circular.

FGS