A touch screen requires a software team, with the associated costs that brings. Over the lifetime of a vehicle, I'd think buttons are a lot, lot cheaper to install and maintain.
Car makers pretty much committed to having a touchscreen in every car maybe a decade ago. Once you have one, any functionality you can move to it is 100% cost saving.
(Though I think the Tesla-driven fashion for minimalist interiors is probably also as important as cost)
A touch screen requires a software team, with the associated costs that brings. Over the lifetime of a vehicle, I'd think buttons are a lot, lot cheaper to install and maintain.