First, expo is still weeks away and I doubt that it's an issue with that. I flew DTW-NRT last week and over 9 seats empty in J and over 9 in Y. Plenty of aisles to go around.
I think the issue is how DL is blocking more seats than in the past or at least what NWA flyers were used to. When I flew the 744's, I could almost always snag an exit row. Apparently DL is blocking them now.

These should be open for elites...