It is not.It really is.
On this route he can cruise to win it without him.
It is about what he has raced in the season and the grueling prep he as has done for each race as well.
After Tour he needs and should take a break.
Going to Vuelta would just be dumb. It wouldnt be a walk in the park and he could suffer in the long run from attempting it, after the schedule he has chosen and done.