Because I read mail from a common inbox. Everything is there, on one screen, for me to check and read as it comes in, without having to folder-jump (my mailer, btw, is pine). Things of low relevance (things I like having a local, searchable archive of, or things I'm on for corporate reasons) get sorted off by procmail. My "inbox" is everything I'm interested in reading. Which (at least at one point) was this list, the nanog list, and most of my personal email.
I can't even imagine working that way. I'm subscribed to dozens of lists, with at least 3 identities, plus lots of automatic mail from servers, and several friends. It all gets sorted by procmail into separate folders and Mulberry displays the folders that have new stuff in them, making it easy to read things in some kind of priority order first thing in the morning.
