Cost isn't the only factor to adding a cooling loop, there's a good chance that they'd have to make room in the pack for the cooling system, which means either a bigger pack or a less powerful pack. As to cost, have to engineer the radiating, plumbing, plumbing mounting, computer controls for the cooling system, and of course the radiator needs good airflow which might require a redesign of the front end, and the charger port is there, so that might need moving which requires more engineering. It snowballs easily.

I actually agree, we leased our Leaf because we wanted an inexpensive electric car, and this was at the height of the Bolt battery mess, so that really only left the Leaf, but we weren't dumb enough to buy it, use it during it's best years, then give it back and let it be someone else's problem.