Are you talking about putting a bunch of 240V outlets in a parking lot?I thought the Rivian was a L1/L2 cable? Is that not the standard?
EVSE allow controlled access, billing to the room/customers if desired, load sharing so fewer circuits/wiring required, and not much more cost if you are retrofitting to add 240V outlets.
Using your portable EVSE comes with the ric=sk of theft as well, and I imagine as EVs gain in numbers that will become more of an issue. Some EVs lock the J1772 while charging, many do not (on a few it is an option).