I think hens, people pressure, and weather play the biggest roles in gobbling either on the roost or on the ground.
A lonely bird, on a crisp clear morning, that hasn't been bumped by people repeatedly in the last few weeks I likely to gobble pretty well.
A hard hunted bird on crowded public ground, who has a couple hens in the tree with him, on a rainy day is probably going to be less vocal.
There are a number of factors but finding him without hens is the biggest thing.
Even on hard hunted land, the mid-morning when his hens leave him, can get him gobbling even if he was quiet on the roost.