Löw probably plans to use Reus or Draxler on the left side and Sane is inexperienced with the NT (actually Reus is as well lol) so I guess that is why he dropped him.
I think this rumor (nonsense) hasn‘t been posted yet: https://www.fcbarcelonanoticias.com/dembele-cillessen-por-salah-trueque-barcelona-liverpool-triunfa-redes-213464-2018-06.php
I could imagine that this was part of the reason he left. If I recall correctly even after winning to Cl in a row there were still people thinking he doesn't have what it takes to be Real manager(?). This would basically mean that if he doesn't win the Cl every year (or e.g. a double), he would...
Today I read somewhere, that he said something like if it were for him, he would definitely renew and that he lowered his demands. (i don't know the source anymore)
Better just wait and see what happens.