Of course, money are guaranteed. It's just like a preseason with more money and exposure. I don't see the benefit in not playing this but playing some friendly games in Japan.
If money at this CWC event wouldn't be serious, yes, I could understand.
Nah, there is a big difference between playing in CWC and friendlies in Japan.
Asian Tour will come after whole squad will rest for at least a full month (most internationals played their last games around June 8-10th and we start preseason on July 13th). We'll have initial first two weeks of trainings in Barcelona (I assume) before travelling to Japan. A work done in physical preparations during those two weeks is a foundation for a successful season. Then in friendlies we'll start to build up match fitness when usually nobody plays more than 60 minutes, introduce new signings into the system and coaching staff will also have a chance to look at how some younger players have developed over last year.
CWC is played without a rest after a 10 months long season and Nations League/WC qualifiying games straight after. Players are physically and mentally exhausted which increase possibility of injuries. As does games mostly being played on bad pitches and in extreme heat. Then players of teams getting far (like QF and SF) will only have 2-3 weeks of real rest before they'll be rushed back to the preseason that will also be shortened. They will have less time to build fitness level and try out different tactical approaches before next season starts and then they'll be back to play three games a week most of the times.
Teams with new coaches like Madrid won't have much time to prepare and try out different things in preseason so will have to do that in regular season where there is always a danger of dropping points. There is not much Xabi can do right now on the pitch to implement his tactics while playing in the CWC. One day they have a game, next day regeneration and then are already on the plane for next game. If he could choose I can guarantee you that's not how Xabi would want his first summer in charge of RM to look like.
Sadly for us Atleti have gone out yesterday so they will have at least some more time to proper rest and preparations. But they will still feel consequences of a shorter summer with less rest.
CWC final will be played at same time when Barca will start with preseason trainings so we will be in ideal situation to start season strong again and put pressure on both Madrid teams from the start. Hopefully this time Flick will learn from his mistakes (if I see Yamal and Raphinha consistently playing full 90 minutes in games we are up by 4-5 goals early in second half again then Flick is just a hopeless idiot), rotate better and also work on improving defensive stability of the team. I think it's more a systematic flaw rather than personell problem so hopefully he'll figure something out. He'll have more than enough time compared to our domestic and also most CL rivals who are now wasting their time and energy playing in the US.
tl;dr Besides money there is really no good argument for wanting to play in this glorified friendly competition so thanks Xavi again.