Batteries can be replaced. An EV that could run 1 million miles would still need maintenance - I think the point is that they could be designed to last.
Planned obsolescence is so wide spread we don’t even notice it, but lots of products are designed to fail either through cheaper components or deliberately flawed design. That means we have to go and buy a replacement. It is also generally cheaper.
So we either have cheap products that will break or seemingly expensive products but they last for a very long time. But in the long run the cheap products generally cost you more to buy than one expensive product.