From looking closer into my AdSense numbers the past couple of months, I've learned that the earnings my site receives from placement targeted ads has taken a serious tumble. My site doesn't seem to be drawing them anymore -- no new ads have been rotating through my Shown Ads page for weeks, and the earnings I'm receiving from placement targeted ads is now in the single digits, whereas once it made up a very healthy portion of my AdSense earnings.
What I'm wondering is, why? My traffic hasn't slowed down this year; in fact, it's grown. I haven't changed any settings in my account -- the ads that I had made targetable are still targetable. Contextual and interest-based ads seem unaffected for my site -- they're earning at the pace I'd expect them to. But placement-targeted ads seem to have fallen off a cliff.
Any idea what the problem could be?