They're quite difficult to use without looking at them, and I've got better things to look at while driving. Better buttons that don't move and have "presence" than I can feel without looking.
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About 20 years ago, every teenager in the world who had a mobile phone was able to select a contact from their phonebook and type an entire message and send, in class with their phone in their pocket.
This is possible because of physical buttons and a deterministic user interface. The same applies to cars and other control interfaces.