The Trilogy was expected to happen in September. GGG will fight next month and Canelo in May. If ever one of them loses on their respective fight, the fans will be able to move on it within 1-2 months. Therefore, after that period, we can expect that there will be another hype for that trilogy until the month of September, the big night in boxing history this year.
Win or lose, that trilogy will happen. It's just that on the side of GGG losing against Murata, it seems not to make sense to make a fight against Canelo if he can't beat a much easy opponent as it should be.
And it really make sense for the fight to happen regardless if they win or both (but it will be good marketing if both are going to win though).
Another reason is that the revenue will be huge for everyone, Canelo will get the lion share of the purse split and now that the whole pandemic is easing, people are willing to go out an spend their money just to watch a good fight like this. So it's a win-win for everyone, money wise.
And maybe this is the big reason why Canelo agreed now, because he was totally against the 3rd fight because there is nothing to proved as he beat GGG already.
But as he mature and maybe by some advise of his close families and confidante, now it make sense because of the money and for his legacy.