A remaining use case is that dedicated physical devices provide dedicated contexts that benefit human memory. If you forgot why you picked up a calculator obviously the search space is obviously smaller (you picked it up to check or visualize some math) and has a discrete context (this is a math device connected to math thoughts in generally) decreasing the "distance" between thoughts even in the search space. If you forgot where you just checked or visualized some math, you have a physical object to be the most likely thing to remember for you.

If you go to open an app on a single device that you do everything on and get lost along the way you have a lot fewer breadcrumbs.

It's probably not a large market that still prefers the dedicated device, but there are definitely users I know who do if for no other reason than mental focus.