Because he's literally been worse than both of them? You're point seems to have been, "look how good he is he should start every game", and you aren't factoring in who/how we're playing and are ignoring how poor he's been previously. Bayern game was a training game for them and Pool we just sat in and defended. All the games we've played Varane in before this, for the most part, he's been appalling this season. Then he got dropped, rightly, and now he's back in the team with Maguire's injury. That's how it should be.
He seems a great guy and in his pomp was immense but you can't have watched us this season, seen his performances and then watched the Bayern/Pool games and forgotten the rest?