They don’t inherently need to, it’s just that with e-reader devices like your examples you tend to either have physical buttons on the side and/or want a place to grip the larger device without tapping the screen. There’s no reason a phone-sized e-ink device would need the bezels. Most likely there weren’t that many screens to choose from and they didn’t want to shrink the keyboard down to better match the screen.
E-Ink has big bezel generally, no?
They don’t inherently need to, it’s just that with e-reader devices like your examples you tend to either have physical buttons on the side and/or want a place to grip the larger device without tapping the screen. There’s no reason a phone-sized e-ink device would need the bezels. Most likely there weren’t that many screens to choose from and they didn’t want to shrink the keyboard down to better match the screen.