I love Messi and my gut feeling is that he was the one who wanted out because after getting a taste of a big cup trophy again this summer (after such a long wait since 2015), he realized he can win a couple more CLs surrounded by a good team. Plus, he can coast in the league for that 2022 WC.
Of course, he was sad that he couldn't be a one club man...so I think his sadness was real. But I also think he had made up his mind he didn't want to be here surrounded by the bum quintet of Busquets Pique, Lenglet, Roberto and Alba (all 5 who might be starters for us this season).