I do wonder how they filled all that air time before the web, social media, email etc. Live phone-ins from viewers?
David Duffield, the original EuroSport commentator when ES was the only channel to show the Tour live, used to fill the time by talking about the food and wine of the region, he used to describe every one of his meals in detail.
This usually lead him to miss all the important moves, crashes etc while he was talking about the 1982 Chateau Neuf he’d enjoyed the previous night.
Sometimes they talk about the bike tech, do a focus on one rider or one team, fill in the gaps with interviews with team managers etc or occasionally do a piece on (say) the Moto Cameraman or some other unsung hero of the Tour. It can be quite interesting when they do that; equally, talking about the actual riding when it’s a 5hr flat transitional stage can be dull as ditchwater.