Why do some bucks never seem to rut?
Some mature bucks do most of their rutting on small, tight ranges deep in cover where you don't see them. Others — particularly cryptorchid or otherwise hormonally compromised bucks — really do skip the rut. But the most common reason a buck "doesn't seem to rut" is that he's rutting on a different schedule than you're hunting.
Excursion behavior pulls some mature bucks completely off their summer property during peak. He's rutting hard — just two miles north on the neighbor's. Other bucks lock down on a single doe in a thicket and stay invisible for 30 hours, repeated multiple times across a 10-day window. The rut is happening; you're not seeing it.
Genuine non-rutting bucks exist but are rare: cryptorchid bucks (retained testes) develop velvet antlers and skip breeding, and some old-age bucks past their peak breed less. If your buck has hard antlers and tested testosterone-driven sign in October, he's rutting somewhere.