Gareth Bale: why doesn' Harry have him in midfield?

He come on the pitch late as a sub but did you see him running through the midfield taking on two or three players.. I reckon he's fantastic and will be world cl in a couple three years and would love him at Arsenal, if Spurs don't reckon he's good enough to start as left back then put hm in the midfield, what do you think... I would rather he stayed then Lennon if I was a spurs fan.