I don't think harvest numbers have much, if any, correlation to the overall population.
And 3 years worth of data does not a trend make.
What I have noticed, specifically in the last 3 years, is a tremendous rise in the number of hunters using public land.
With greater hunting pressure, the turkeys become extremely hard to kill.
I have hunted turkeys on public lands all my life, and killed a gol-dang bunch of them, but when they are harassed every day of the week they become almost unhuntable.