I guess the part I don't understand is the target audience. Who is so serious about writing that they need a full-screen editor, but so unserious that they don't have a favorite editor already? I've published two full- length books and posted a hell of a lot more than that, and you can pry my text editor from my cold dead hands. I'm not even going to mention which one it is; it doesn't matter. Switching to a new one would be a frustrating and painful experience that would get in the way of my writing for weeks, maybe months.
Via decafbad.com [1], “Mark Pilgrim: wrongroom [2]”
It could also be “because I can.”
Or because the software being used sucks [3] and it's easier to start over than try to work on an existing project.
Any number of reasons.
But I can certainly relate to the trauma of switching editors. Heck, it was traumatic switching email clients [4] and I'm still finding flaws in mutt [5] (just last night, I patched it to change the default location for saving attachments, since I hate cluttering up my home directory).
[1] http://decafbad.com/blog/2007/01/23/is-this-the-
[2] http://diveintomark.org/archives/2007/01/21/wrongroom