The finance has already written you a check, they’ve already done all this leg work.
You’ve already driven it, if you’re purchasing it in earnest you might have already invested in charging infrastructure for your home, a whole laundry list of friction.
Then there’s what happens to the car you returned.
I wouldn’t want to be the guy stuck with a car that went through multiple 1000 mile “test drives” with Tesla’s reconditioning track record of delivering cars with toe nail clippings in the seat rails
(traditional dealers do have offers like this from time to time, but it’s exceedingly rare they’ll actually let you keep the car for more than a few hours, and most importantly they don’t require you to buy the car first, they’ll take a deposit or let you rent the car)