Premium Economy

So, I've checked in for my flight later today and it doesn't look as though I've got an upgrade based on my seat placement.  I shouldn't be disappointed, but I really am - because I've been spoiled by multiple upgrades in the past.  At least I'm in premium economy rather than plain old economy, but I'd much rather be in business because that is a significant step up for a nearly 10 hour flight.  I've been wondering if I've done anything differently that hasn't warranted an upgrade - does it make a difference that I booked my ticket much earlier than usual, that I checked in online not long after online checking opened, that I'm flying on a Sunday, that I'm not flying as close to Christmas as I have in the past?  I suspect that it is more likely that Seattle, and more people in Seattle, are so much more affluent than they used to be, so there are probably less free seats in business.  Shame.  I haven't even got a window seat in the premium economy section because none of them were free.  This, combined with the fact that I've got a nagging headache from yet another restless night, could mean a tough flight...