Whereas i agree that the bezel is in part due to technical constraints, i would like to say that there are some functional as well. For example, on a edge-to-edge screen it is hard not to block content with your hands while holding the device in a natural way. While unintentional presses can be resolved through smarter detection, blocking of the screen by our physical attributes is a harder nut to crack (ok, we can use projectors and such to make our hands appear as transparent, but lets keep realistic here).
edit: that said, someone will surely sell edge-to-edge devices in the somewhat near future. plus: worst case, you just use a soft-bezel when needed. Just saying that the bezel has functional dimensions.
(Aesthetical too for that matter, as evidenced by the use of passpartous).