I’ve heard the explanation before, but when’s the last time you had a blind guy in the back seat of your car who had to make it to an ATM?
I don't know any blind people. But I'm aware that they exist, and that they have friends with cars, and that they ride in taxis. I've also known people with various forms of disability, and most of them want to be as independent as possible.
Of course, they're a tiny fraction of the folks who use drive-up ATMs, but making the buttons bumpy is a tinier fraction of the cost of building a drive-up ATM.