Or private detective--outside of British imports of course. Medical dramas. Etc.
I think I probably agree with you though that Westerns (both on TV and film) are probably the almost stereotypically American genre that used to be hugely popular and is largely non-existent today.
But I'm not sure I'd assign any great significance to the fact other than shifting tastes and, perhaps, sensitivities.
To refresh my memory, I just looked at a bunch of years of network programming. The 'rural' comedies don't seem to make that much of a footprint. If anything, a person could probably build a more convincing, invented-from-whole-cloth, essay about the birth and death of Western TV shows.