There are a few reasons I think: Battery packs are often now integrated into to structure of the car as well to save space, weight, and help with crash ratings

There are a few reasons I think: Battery packs are often now integrated into to structure of the car as well to save space, weight, and help with crash ratings. EV batteries also require more than just an electrical connection. Most EVs (besides the Nissan leaf) have liquid cooling/heating so you'd have to manage those connections as well. Many EVs have different size battery packs as well. It would be hard enough to manage all the inventory swapping one type of battery, let alone 50!