“If Wan-Bissaka is so good defensively why do teams attack down his side more when they face United?”

Well, the answer is simple:

Teams attack down their left more than their right generally — against any opposition.

I am mapping this out now and will tweet when it's done.

I do not know the reason. However, I suspect it is because right footers tend to be on the left-hand flank/wing and most teams are filled with right footed players. As they like to contribute to goals more directly, it results in the ball moving to the left side even more.

In addition, quite a few teams have offensive-minded FBs who are able to push on down the left — e.g. Chelsea with Alonso, Everton with Digne, etc. This adds to the left flank which is already utilised.

Thirdly, and this is untested, teams could have more left-sided CMs who like to play in the half-space on the left as opposed to directly in the centre. So, it results in that side being used more.

Nevertheless, to question Wan-Bissaka's defensive capabilities with the argument of “why do they attack down that side then?” without factoring in the multitude of other and more predominant reasons why teams do that — against anyone — is reductive and insincere.