No, casting is simply a better technology. Its better no matter what type of propulsion you use. Its just that other car companies, unlike Tesla, were not willing to make the massive investment it required to make truly huge castings. Smaller casting have been in use before on various cars, some Audi had a decently big one on the wheel well.
For Tesla to do this they had to work with a company that made the largest casting and task them with creating a massively larger casting. Tesla material teams also developed its own aluminum alloy that wouldn't bend as much during cooling. This allowed Tesla to not have to dip the castings into a fluid to cool them.
Castings had been used by car companies for a while, sometimes decent size ones around the wheel for example. But Tesla took the idea and put in the effort to take it way further.
They started with doing only half the back, and then bond the two sides. When the company finished development on the larger generation of machines they pioneered doing the whole back piece all at once.
See: https://electrek.co/wp-content/uploads/sites/3/2020/04/Tesla...
> Also, because Tesla is so popular, is it possible that its attractions have far less to do with the environment and more to do with everything else about the car?
This is clearly the case. People never by things 'just of the environment'. Tesla produces the arguable the best price to return for EVs. At least unless you want a much smaller shorter range car.