The reason they do this is simple, money. It is much easier for a manufacturer to produce a single screen that contains all the functionality that can be adjusted on the fly using software. The alternative (and the way it has always been) is early in a car conception, to design the cabin with the buttons layout, design the switches, find a manufacturer, test the switches, test the layout, repeat, etc… Plus if they find a flaw in the cars button design / layout late in the process, it becomes even more expensive to fix. Nowadays, car companies have an excuse to use screens, not only does it save them money, but they can disguise it under « modernism ».

Disclaimer, this is from what I heard and using common sense, but in might be completely wrong.