What do you suppose it is about the ECB set up / expectancy of our test captaincy? Okay, so Cook managed to hold on to most of his form when he became skipper, but we can go back to Botham, Flintoff and now Root, whereby all their natural talent is stripped away from them as soon as they become captain of the test team.
Do other countries have this issue? Certainly not with the likes of Smith and Kholi, even MS Dhoni continued in his rich vein whilst captaining India. Alright, it's not an absolute, but when Root was selected to be captain, my heart droid sink a bit as the tendency to score next to **** all looked on.
Happy to be proved incorrect with stats, but sometimes, it's not about the best player, who makes the best captain, S Waugh being a prime example. I'm sure there are many examples of fine English cricketers who became the test captain and continued to either score big or take wickets, but, unless we go back to the mid C20th, none are springing to my mind.