Again, PvP content has its own team producing PvP content. Currently they're rehashing Frontlines as much as possible, to the point where we even have an entirely new map for 3.0. Most of us who actually use the content they produce would rather have something relatively simple (duels) than a repeat of Frontlines (Slaughter).
Those of us who actually use the content they produce realize the issues with it (ridiculous queue times) and would rather they fix that instead of adding more modes to split the community over (which just makes queues worse), but failing that we'd rather have something that is very easy to participate in and provides instant PvP gratification. Duels is that content. It requires one other person. If we want to practice, 1v1 balance doesn't really matter. If we want a serious match we can balance it ourselves.
Pretty much the only legitimate reason against duels I've seen is that PvEers are scared of others harassing them. Apparently they all ignore the fact that this doesn't happen already. When was the last time someone harassed you to play Triple Triad with them? Duels don't even need rewards like Triple Triad, so without that there would be little reason for someone to "pick on" someone who doesn't PvP (if duels equated to quick and easy Wolf Marks, I could see people spamming requests with anyone to get an easy win, but I'd suggest duels having no rewards). It would just be something PvPers do while waiting on those 30 minute+ queues.