The problem with Maupeou, was his lack of true political base : initially he was part of Choiseul's (I personally think Choiseul could have been just the right candidate for a Prime Minister*) general base until he was eventually favoured at the latter's political decline.
Without a bit of political support (and critically in face of a general opposition from provincial nobility, high nobility, bourgeois elites, etc.), his reform would have been really hard to fully implement.
Maurepas had an easy time replacing him with Louis XV's death, critically with his closeness with Louis XVI (not that Maurepas was particularly incompetent, but his policies asked for a bit of social support from nobility)
*Let's hope the thread won't devole into a Choiseul vs. Maupeou discussion