Most Model S owners never or rarely if ever use SCs.
Half the Model S fleet (perhaps less now) doesn't have AP convenience features.
Iacocca initially released the Mustang without a radio in the base model, because he wanted the car to appeal to families as an affordable family car.
It makes sense to have a base Model 3 with neither SCing nor AP convenience features enabled - but enable-able at any time by anybody for a one-time $1000-$2500. For some people, it's easier to get a monthly payment they can work with up front, and to then save for one-time expenses without paying interest thereon for years. Remember the target demographic.
Many metropolitan Honda Civic and Toyota Corolla buyers don't leave a 50-mile radius, and if they do, they fly.
That said, of course others will order the car fully loaded with every conceivable performance and comfort option. Fine and dandy. But I'd be kinda annoyed if I had to buy features I wasn't planning to use much if at all. And some people are perfectly happy waking up every day with a full charge in their garage, carport, or driveway, and they have neither the time nor energy to take road trips for the heck of it.