I bet it just happened organically. Started as an A…Z list but then someone had to implement it so that it cycled.

And the simplest solution at the UI level is to make it a finite list that cycles multiple times. And that simple impl required no updates over the years despite changes to the UI toolkit.

e.g. compare the HTML solution to one that is a virtualized JS infinite list. The HTML finite list solution is trivial while the infinite cycling one probably needs to be ported when you change frameworks (like move to SwiftUI).