I don't know what is going on either, but we are experiencing the same phenomenon down here in southern NM, too. I think our problem is that we have so few two-year-old gobblers because of the poor hatch year before last that most of our birds are older age-class birds.
There are fewer gobblers competing for lots of hens,...meaning the gobblers that are here have all the company they can handle,...and the older gobblers have learned that keeping their mouths shut lessens the possibility of uninvited attention from predators,...and hunters.
Regardless, it is not a reassuring feeling to see turkey sign everywhere, know there are gobblers out there, and not be able to have them make a peep in response to your calling!