You do not work in marketing I assume?. Even different brands from the VAG-group don't want to be seen as partners. Audi, VW, Skoda, Porsche all have different buildings/showrooms (often on the same plot). They don't share a single thing.
No way in hell Mercedes, BMW or Audi will tell it's customers they can charge at Tesla's stations, confirming that their network is superior.
After all, for European Car manufacturers, Tesla is the big enemy and primary competition in the EV segment. They even proposed a new incentive today, for cars with more than 200km range and no longer than 4.68 centimeters. Guess what, Model 3 is 4.69. That is so obvious it's sad.