D&D and Warhammer killed off ye olde wargaming I think.
I think the appeal in those two over historical games is the variety they offer. For example, in 40k you can fight as, and against, everything from regular humans, to genetic super soldiers, to giant alien beasts, to horrific demons from another dimension. In a historical wargame, it's just going to be regular humans that are roughly the same in appearance and capability.