And one assist only.
I know the stats, but he played most of his Internationals almost 2 years back as a kid, and mostly as substitute. In total, he has played less than 600 minutes in 12 games - that's just about a half/game. In last one year, he has been outstanding in Pep's system and he could have added exactly what was missing in this German team - pace & width. Even after a bumper season at MCity, his goal tally is 15 from 58 EPL games for a free scoring MCity side (broke all sorts of scoring record this year), therefore goal/game isn't the best KPI to look for Sane.
Also, if you have seen 3 German games, it's not that they were dominated, rather they had over 60% possession in every game (75% against Korea), but that possession was lot in mid-field; and because of lack of pace, teams kept a high line against them and narrowed the midfield where Germans were dominant. Muller, Gomez are tortoise like slow these days and basically a target man - in WCs, team don't allow that much space for these type of target men; you can see Giroud's goal scoring record in friendlies & tournaments/qualifier for French team. If Germany had someone with the pace & dribbling skills of Sane, he could have allowed German mid-field more space to push through balls for him & Reus.
If you ask me, I know exactly the reason, but can't prove - so don't catch me on this. His father is French (Senegalese) black, his mother is a pure German blood ...... and he is a cross ... Sane made a blunder by not opting for France.