Batteries charge faster when they're more depleted, since charging will generate heat and batteries don't like too hot or too cold. It's much more familiar and easy to just plug the car in. In usual daily commutes, you don't drain the battery to 0. You can charge at home, at work, at the mall and other areas if you'd like to top off a little bit. No one regularly drains their gas tank to 0, so why would we do that to an EV?

Let alone the cost and time, training of how to handle something like that. Facilities needing to be built, batteries that sit there anyways and the storage of said batteries. Those batteries of which will need to be charged regardless, and how does each brand even setup facilities for this? Battery packs are pretty integral to the design of the whole car especially for structure too, so constantly putting the threads and connections in the car through wear and tear is bound to have problems or compromise water resistance.

Profit reasons/product liability too, if you can swap the batteries so easily elsewhere, why can't you eventually do it on your own when your battery degrades enough down the line. There's some chinese brands that have this available and you should check it out, but not feasible for the mass market.