Have you watched Pogba play at all? Technically excellent but incredibly naive tactically, especially in terms of his positioning and defensive responsibility.
Now that day against Blackburn both Park and Rafael played in CM because we were missing a whole defense and therefore Carrick was forced to move back into CB alongside a positionally suspect Jones. This weak and unfamiliar defense needed some cover in front of it and SAF obviously thought, rightly or wrongly, that Park and Rafa would cover the back four more sufficiently than Pogba could in a midfield two, and that the team he put out would be enough to win the game. Its obvious things didnt work out that way but it could easily have gone differently. I don't necessarily agree with his selection that day but I can at least see the logic behind it.
Anyway im just pointing out its nonsense to suggest that this game played any part in his decision to leave us, and if it did I wouldn't want his defeatist attitude here anyway. I think Pogba's motivations are clear when you see Juve's midfield options and compare it to ours, he's not leaving for playing time thats for sure.