When you are breaking into an industry or trying to position yourself you need to hit above your weight. I remember when Volvo made their move, they went for the safety angle as well. Tesla has always been dogged by members of the industry and instead of turning to marketing speak Tesla turned to established and trusted entities to show their cars true value. Now it can be claimed by getting into the gritty details as they did in their blog they are entering the realm of marketing speak. (disclaimer, I own a 3).

With regards to why aren't all other manufacturers doing as well, just glancing through the web site of the NHTSA I cannot figure out how they decide what to test. In their current list of vehicles to test I do not even see Tesla so I will assume manufacturers can submit cars independently of being requested by the NHTSA.

Now when comparing cars at https://www.nhtsa.gov/ratings we only get stars which four is pretty common in the price range but you can compare and find cars that have the same star rating. Volvo's tend to still get 5 stars across the board