Last season, the birds really shut up in my area. I saw them on several occasions with hens, and I saw one go into strut every time I called.
I also saw more predators than normal last year, and have to wonder if the birds stopped calling cause of that. Or maybe it was just that they were already with hens...
I also killed a bird this year that did not gobble. I heard him drumming behind me, but he never gobbled. I actually got him pretty early, and have an idea where he was roosted, but even on the roost he never made a gobble.
Tough to hold out when you do not hear that activity... I knew birds were there, but if I did not have that confidence, I would have probably packed up and looked elsewhere (missing out on a productive hunt).
My buddy has access to some property that was loaded with birds before the season, and has not heard a single gobble. He is certain they have moved out, but I think they are just not gobbling...