It’s hardly a danger zone is it? There is no military reason for him not go so I wouldn’t see it as a military excuse.
He does want to go.
They’ve already more or less ruled out allowing him to serve in combat (his brother, as the “spare” is a combat soldier, the heir therefore cannot be - maintaining the succession is considered important), and so he went into S&R in the hope of actually being able to have a genuinely useful military career in a non-combat role. Now the government is raising blocks to that.
Like any junior officer, he must obey orders - he does so, but he doesn’t have to like it.
You don’t know much about the Royals.