It's really just "battery" longevity. The EV-unique part of the power train on most of these vehicles is a single-gear electric motor with one moving part. There are broadly similar devices in service today that have been working more or less unmaintained for literally a century (think elevator motors in old apartment buildings, etc...). It's pretty well travelled territory.

But yes: batteries age and need to be replaced. But while that's quite expensive in materials, it's actually very feasible as a maintenance task. A 2012 Model S could have its battery swapped and no doubt drive for another decade with minimal fuss.