While I agree that Matic has actually played alright when called upon recently, he had made it clear he didnt want to stay around given he was behind McTominay, Pogba and Fred in the pecking order. Therefore the other three fit senior players who better fit the direction of the club, play.
You don't put him in the squad as if he's an equal part of it, then treat him like he's not an equal part of it, and expect the fans to figure that out and understand. That makes zero sense.
Solsjkaer must simply believe the others are better starting options than Matic at the moment, rightly or wrongly.
Do you really think managers should ignore the players attitude towards staying at the club when picking their teams? Obviously there are cases where some players are better professionals than others but Matic commented "? ?" on a benchwarmers post linking him to Jose at Spurs in November, and since has not committed to staying here.
And then if Ole was to drop him totally and then Andreas or Fred becomes unavailable, he would have lost his focus completely and Ole will be forced to play a kid (not the worst option but better this happens at a controlled pace).
I do think that Matic would be a better option over Andreas but he just isnt as committed and thats what Ole wants to encourage.