[yoz]

For the same reason that we prefer typing on a physical keyboard instead of a flat touchscreen. When you need to type for more than a few minutes, screens can be exhausting. This device is aimed at people who use them for hours every day.

Also, unlike a phone, the advantage of a single-purpose device is that it doesn't need to be switched back to the right app, is unlikely to crash, and isn't something you depend on for a whole load of other things in your life.