Right, the data says that.

But there's something screwy about the data, because it is generally much more difficult to find Skymiles award seats. Everyone's individual experiences are anecdotal, but try it yourself: take a domestic city pair a few months in advance and try it on Delta and United. See what happens.

The only thing I can think of is that more people are trying to book award travel on Delta, or are willing to pay more miles for the awards.

It's also possible that Delta is better at making seats available close to departure time. As I indicated, I generally book award travel months in advance.