At the casual level, games don’t last for nine hours because people would get bored long before that and would want to move on to some other game. That’s not relevant to people for whom it’s literally their job, and who will get fame, prestige, and money for winning, even if it takes hours. Plus, you’d end up with games being decided by who had the greater physical endurance, which is a heck of a lot more “impure” than putting a clock with a couple of buttons next to the players.
That argument makes zero sense. None, zero, zilch.
I wonder if most professional players would actually prefer to play that long, if given the choice. I see no reason why they couldn’t get the same fame, prestige, and money for Rapid Games. If the World Championship were Rapid instead of Classical, I bet it would get more viewers and thus more sponsors and thus a bigger prize fund for the winner.
Correct me if I’m wrong here, but …
Isn’t it now true that in a high-level chess match, the players must be isolated from outside contact and games must be completed in one sitting? The reason is that computer analysis is now so valuable that it must carefully be excluded to ensure a fair match.
If this is so, time control is essential to produce a complete game within a time that is acceptable.
This illustrates perfectly why Carlsen offered a draw in game twelve when he had a “very likely” win. He opted for the “absolutely certain” win in the tiebreak, instead.
And I disagree with you. 
Among the people I play chess with, we don’t use any time control. You sit down with some beverages and snacks, and chat and watch and play. Just like any other table game. You don’t have time controls for chess any more than you have them for other board games or card games.
For live broadcast, I can see why professionals want to go to a faster format. That’s because they want to commercialize their games and get well paid. There’s nothing wrong with that and I’d do it too if it were my profession. But it’s not because they want to play the best chess they’re capable of.
But that’s not really a comparable situation to professional chess. You might not have explicit time controls, but there are implicit ones. There is social pressure in your games to not spend 30 minutes on every move. If someone was routinely taking excessive time for each move, you’d probably razz them a little, take them aside to talk about picking up the pace, or find someone else to play against, depending on your relationship to the other player.
Some kind of time control is necessary in professional chess. I think playing only rapid games in a championship is a mistake, but I’m fine with using them as a tiebreaker. And if the next few championships result in 12 draws through the standard games, maybe there needs to be a little more time pressure in them.
For those preferring the faster time controls, the World Rapid and Blitz Championships start in less than a month. I think it’s great to have both, if there’s money available to support it. The rapid & blitz tends to have the opposite problem to the classical, in that there is too much happening too quickly to follow anything, and many games get decided on huge blunders. It is fun to watch though.
What’s really absurd are the Bullet games that only have 1 minute per side! While I enjoy fast chess, that’s a little too fast for me. My preferred range is 5 minutes to 30 minutes.