Because hes a good player probably?
He isnt the flashy Hazard or Brazilian wingers of past, but there is a reason he plays for Brazil, theres a reason he starts for us, theres a reason nobody(in power) wants to give him up, and theres a reason why one of the biggest clubs in the world keep trying to get him. You know what you are going to get from him the vast majority of the time, and in a world where Cuadrados,Alonsos, and Moratas are prevalent that means something to have a consistently high level(Note:not the highest level) guy like him in your squad.
His documentary series on Youtube is pretty good too: