Rooney was an instinctively clever player, so he didn't really understand consciously why. Hence why he's so shit at teaching it to others - he can't get into the same headspace as someone who doesn't do stuff automatically.
And you've missed out the most important bit of information - whether Kenny Jackett was a clever footballer.
Don't want to be harsh but how does anyone hear Troy Deeney speak and think he is manager material?
Same goes for Wayne Rooney. Neither were clever players. both played best when worked up, on the edge and playing on instinct. Excellent at what they were good at but that is just not what is required for leading a team.