Between when Tesla introduced S/X with 100 KWh battery packs and when they decided to standardize on 48A charging, there was an option to purchase a 72A charging upgrade.
And Tesla actually installed the 72A chargers in at least some of the S/X models built in that period, and then software limited to charging to 48A.
When I checked with Tesla, they verified our 2017 S has a 72A charger onboard, but to do the upgrade from 48A to 72A, we'd have to pay the same price to do the upgrade as if we only had the 48A charger on board.
Our 2018 X has a 72 charger, and we charge it on a wall connector set to 48A (on a 60A circuit), and that charges fast enough overnight.
So far, we haven't used the 72A charging capability on the X, since we charge at home at 48A, use superchargers on road trips, and use a 30A dryer outlet when staying with family.
And this is why Tesla likely decided to standardize on 48A and reduce the cost of the onboard chargers and the mobile connectors.