In reply to Tyler:
It's probably three issues - his 'moderateness' means he doesn't attract media attention, his lack of BREXIT appetite, and that he was associated with May as being the 'pair of grown-ups'.
I like him, he was a very good Defence Secretary who grasped both detail and numbers - he was also very highly regarded by the CS in the Foreign Office...
If it weren't for his slightly 'grey man' thing he'd be not just the top choice, but the only choice - in the last seven years he's been cheif secretary to the treasury, Transport Secretary, Defence Secretary, Foreign Secretary and Chancellor - if that doesn't qualify as being a Big Beast, what does?