The Candidates tournament has some seemingly arbitrary qualifications that players must meet, and you could argue that the format doesn't necessarily produce the strongest player to challenge the world champion.
The World Championship match itself is problematic because it gives the defending champion a fairly huge advantage, in that they retain the title if they can draw out the match, although more recently it goes to rapid chess tie breaker rounds. So in practice the Championship is decided by these tie breaker rounds, which doesn't really seem appropriate.
Given the prep time players have and the engines available, players go into these matches extremely well prepared and draws over the board are quite a typical outcome unless someone makes a mistake.
I believe Magnus wants the Championship to become a knockout tournament to reduce the advantage that so much prep time can give. There is a big difference between prepping for a field of 12 players versus prepping for a single opponent.
This has not been the case for quite a while. All of Carlsen's matches (Anand, Anand, Karjakjn, Caruana, Nepomniatchchi) had tie breakers in the format, to determine a guaranteed clear winner. The Karjakin and Caruana matches were decided in this way.
An athlete can spend all day in the gym and then grab a shower and roll into bed. They may be sore as hell from head to toe but they will be so exhausted they can just pass out and get a great night's sleep. They also get the benefit of endorphins which make them feel good and rewarded for doing their exercise.
On the other hand, a chess player spending all day going over variations and practicing is going to have a difficult time sleeping with all of those lines and positions flying around in their head. They will be mentally exhausted but still active and alert. It is an absolutely miserable experience. So to prevent it you need to cut back on the hours which means spreading out the preparation over many days/weeks/months. It can also get very boring because you don't get the same rewards you get from playing and winning games. The only reward comes when you finally get to the WC match and then you actually have to win or it's utterly heartbreaking.
This is time that could be spent playing tournaments.
This would be okay if the world championships was every four years, but it's every two, so a large fraction of Carlsen's time is spent preparing for this one match that everybody knows he's going to win anyway.
It's similar to the way that many professional teams are reluctant to allow their players to play in the Olympics (in e.g. Basketball, Ice Hockey, and Olympic Football is completely neutered). Carlsen clearly feels that the World Championship is not important enough to sacrifice a large chunk of his career for.
Which other tournaments are considered like the top levels of Chess competition, and what are the criteria for being the top chess player in the world(If not winning the world championship)?
And Carlsen absolutely dominates the others, and have been the top rated player continuously for a decade. So no questions about who is the best, WC title or not.
Carlsen is right now 98 points above Nepo, the challenger, which is an insane difference.
The problem is that the world champion is out of play for 6 months out of every two years, preparing for just one game.
It's boring for him as well as the fans to spend that much time in isolation just trying to memorize everything about one particular opponent.
It would be better to have him out and about playing tournaments and beating lots of different opponents.
Is it because its stressful, and demands too much work and prep from participants.
Just asking as competitive sport at the top level be it chess, football, or even swimming for that matter demands lots of work and a kind of work ethic not easy for most of us.