It's the, "But wait...there's more...."
I don't know the size of their software team, but I suspect it's not small.
They can do more than one thing at a time. And as much as some managers would like to believe otherwise, developers are not fungible. And as others have mentioned, the man-month is mythical.
The upper screen is in a great place for the driver's seat, and the center can show any aspect ratio without letterboxing. It would actually be a great place to watch CinemaScope movies.
I'm not sure where I saw it, but I had the impression the movies could (future) play on all three screens.
As for watching on phone or tablet, it's often hard to find a place to prop up a screen in the front of a car. We have the tray tables, but that means moving to the 2nd row.