I think Chelsea and José were ok with letting him go, José just needed some cover when we play a lot of games so he let Mata decide if he goes or not. We did not need Mata, however we need Hazard. I also think José knew that Arsenal would be a more likely contenter for the title than Man U so he did not let Ba go, but Man U are really fucked (compared to their standards) so he thinks letting Mata go there won't change a lot for them (almost every pundit agrees aswell). Man U aren't even a rival now, we played them 2 times already and their title hopes are gone.