Robertson is limited but apart from his crossing another thing he is good at is timing his runs on the inside. There were a couple of opportunities to do that but Coutinho wasnt bothered.
He also wasnt bothered working for an opportunity either. Now this may be completely Klopp’s fault and he may want a rigid system but Coutinho did nothing with his movement to make half a yard. He could have popped up higher up the pitch or on the right.
Instead he parked himself in the middle and basically said to everyone look how great i am as i try to dribble past my opponent and play a through ball in the middle.
Timing his runs on the inside to then do what? First, he wasn't doing at all when he signed and has only recently started coming inside. Second, when he receives the ball in those tight situations, he frequently mucks it up. Contrast this with Moreno who often gets the ball from Coutinho in those situations.
In the first half, he played on the left of a 4-4-2. It would be a massive issue if a player decides to vacate his flank and move over to the right with no one to cover him. In the second half, he popped up in the right frequently.
As for not going higher up the pitch, I think you've only proven my point about how useless the rest of the midfield is. If he goes further up, who is going to pass the ball to him? This has been our biggest issue for years now. Cut out the supply to Coutinho and he has to come deeper and deeper to receive the ball, which takes him away from the areas where he can cause damage. That's not on him. That's on our other midfielders.
I'm not sure what you expect out of him really when you seem to not be acknowledging that he is not surrounded by players of a similar skill level with the ball in midfield. This is why he is not as effective as a midfielder and it's got more to do with our other midfielders just not being able to play in tight spaces.