[ummonk]

The process of scribbling characters with a marker on a whiteboard is quite tedious and takes up a lot of time and effort. And doing it feels more akin to multitasking than a normal coding process, since so much of the effort goes into scribbling out things (as opposed to the actual coding process). Ability to draw glyphs on a whiteboard will become a confounding factor here.

Being able to type out things in a text editor simply makes the interview process much more efficient.

Note: I share your annoyance with people who gripe about whiteboard problems and algorithms / data structures problems not being representative of everyday work.