I'm going to guess that it probably had something to do with the location of the TV show. Building a set with electric stoves and burners is a lot easier than running gas lines. Plus, lots of explosive gas around the electrical nightmare that would be most studios in the 60s and 70s would probably be a bad idea. This is all just a theory though. I know at the TV station we used to work, they used an electric range for mobility and safety, but that's small market TV, not "The French Chef."