Exactly the same for Gerrard, Pogba, Ali, Coutinho, Pedro, Hazard and many many other attacking players....because they are attacking players!!!
Yeah, Hazard and Pedro - two wingers - aren't as good at defending. Neither is Sergio Aguero, but comparing apples to oranges here.
Gerrard, Pogba, Alli and even to an extent that ladyboy - they all track back and run, put a foot and a tackle in, at every opportunity. Remember when Ross did that more than once a month? We have to accommodate him to be Ross Barkley by putting a million other players that are willing to do the hard work because he just doesn't. Never did, never will, at least not on a consistent basis. We can't have a midfield behind him giving him the ball - Koeman's addressed that by putting other players in slightly more 'free' midfield positions - Davies has done okay for the most part, for example, and it's what Barkley should be doing - being a presence *off* the ball too, not just on it. If he's only doing 50% - hell yeah he'll be predictable and doubled up on. Any team will know that he won't try to win the ball back and get half-arsed when chasing.
From your examples - Pedro actually doес a lot of work up and down the field, despite it being from winger positions, yet still manageс to score loads of goals and all that.