If stainless steel is so great why don't other automakers experiment with it?
Well, we already know why: difficult machining, can't be made into complex molded shapes, can't be painted, can't be color matched, sucks up fingerprints like no tomorrow, difficult for body shops/repairs, reduced pedestrian safety...
And what are the benefits? What does the customer get out of it?
I don't know any group of automotive engineers who would choose Stainless Steel given an "unlimited budget/creativity" type of project. You don't see it in million dollar exotic cars or anything like that. The fact of the matter is that Elon Musk is stuck in the 1980s and wanted his own DeLorean truck.
The issue with SS is that it required new-to-the-world sized equipment and presses that traditional auto didn’t want to experiment with.