I think he does track back as much as he can. He just lacks the stamina to do it continually. He's been superb of late but is really a 60-70 minute player in end to end games.
Completing so many take-ons is tiring. If he was recycling the ball instead of sprinting, he would last 90 minutes. His intensity is on a different level to anyone's else.
Still, he played over 80 minutes at Arsenal, 90 vs Napoli 3 days earlier. If the result was just 1:0 City, he would have played more minutes. Pep is managing his playing time brilliantly.
Those saying, he was fantastic BUT...are being negative. There's no BUT regarding one of the greatest big-game performances in the last 10 years or so.