The average age of a car on US roads is 12 years. Most of those cars in line at Costco are owned by people who probably can't afford a newer car. And many of those who can afford a new car are ignorant of what Tesla is offering, are too timid to go for something that new tech, or are too conservative to go for something that hippy. There are many reasons people aren't driving Teslas. Though if something happens to drive up oil prices I expect demand for electric cars will go up sharply.
Maybe this depends on where one lives, but before I got my model 3, I filled up my brand new BMW 435 for 3 years on costco gas, and my wife fills up (still) her 2019 X3 M40i with costco gas. Additionally, in my neighborhood (temecula,ca), it was much more common to see BMW / Merc / Audi / Porsche (new / newer), than "some hoopty".
The costco close to me usually averages 20-30 cents a gallon cheaper than other stations, even for the premium my previous car (and wifes current car) took. With gas now in our area well over 4.00 a gallon, and a typical fill up in my car being 13-15 gallons, simple math says the gas car saves $4.5 a tank.
I had to fill up my commuter BMW 435 every 3-4 days so roughly $30 a month, for stopping at costco in the morning to get gas (I refused to go during the day when those lines were long).
I am saving a lot more driving my model 3P, but there was also a large outlay of cash to get there. The car itself, the wall charger, electrical installation in the garage.
I always wonder why people feel like these type things have to be "either / or". Why do we have to attempt to "look down on" people who are not ready to drive an EV yet? Not much different than how people talk about Teslas on the BMW boards I am a member of... I dont get it from either side....