Why do sellers assume that the buyer should contact them first to settle a dispute. Isn't that what the dispute resolution process is for?

I use dispute resolution process as a last resort.  Communicating any issues with a seller is just common courtesy to me (do unto others . . .) .  If a seller does not work with me in trying to sort out issues without going to the dispute process then I do a dispute.  I have found that when sellers respond to messages we have worked things out without formal dispute resolution.