Tesla is not your regular dealership. Car purchases are made online anyways.
Carvana has a similar model for used vehicles, and they are very successful with the demo they cater to (buy online or in app, with a test drive period after purchase if you want to return the vehicle). People hate the traditional dealer sales experience apparently (half tongue in cheek, it's terrible, it really is).
It blew my mind when I went to a dealership that had radio ads about their great lease deals on a Chevy Volt. I walked in, told them I'd like to lease a Chevy Volt and that I was very excited about the deal.
They spent an hour trying to talk me into other cars and the sales people didn't know the first thing about what made the Volt so special. GM apparently didn't either since they discontinued it.
Contrast this with my first car buying experience where the 'finance guy' told me to 'get the fuck out of his office' when I explained him how he was manipulating the loan date payment, and price to charge me more. The deal still got done, but it was with the sales guy running between me and the finance guy basically relaying me saying no.
And, frankly, this is how most new car purchases work. Every one I've purchased or been a part of; they don't end with you driving off the lot in a new car, they end with you waiting a week or two for the car to be delivered. I imagine some dealers have a limited stock of new cars in common configurations, and you could drive off in one of those, but that's the minority of purchases in my experience.
Around 15% are factory-ordered - typically luxury brands. An additional 20-25% are sourced from other dealer inventory, or an upcoming shipment that is already specced and on the way. The rest are on the lot and ready to go with the buyer. Dealer lots are huge in most of the country. Endless seas of near identical cars with minor variations in options and colors.