#3 Consistency
If you had to choose between two players - one whose performances can range between 6 and 8 out of 10 or the other whose performances can range between 4 and 10 out of 10, it is a no-brainer that you pick the latter when you go to the WC. Unfortunately, Sane belongs to the former category.
Even during his best season (at City), there were a lot of games where Sane comes across as frustrating. Whether it is a pass during a counter, or not releasing the ball when a teammate is in a better position, or simply being offside, Sane has his fair share of bad days.
The only problem is that Sane's bad days are worse than the average player's. With such a scenario, it makes sense for Low to pick someone like Rudy over Sane, Rudy who is the definition of a squad player - does what he is asked without any questions.