I think Messi should not have considered his commitment to the club economically. They could have agreed on a symbolic figure, since Messi can still earn big money through advertisements. Barcelona might not be able to give him the salary he wanted, but I would expect him to be more loyal to Barcelona.
What more loyalty do you expect him to pay to Barcelona than he already done. After spending more than half of his football career age with Barcelona, won a lot of trophies for the team and make the team to still hold on to their prestige, I would say he had done a enough for the team and they should appreciative to him for the rest of his life because he will forever be a living legend to Barcelona as long as the club is concerned.
When people troll him about loyalty, I just don’t know why that is being brought up, sometimes I think the enemies of him share this talk more to make people hate him instead of liking and praising his achievements so far for the team.
Everyone has a retirement plan and if Barcelona not being able to give him what he asked for made him not consider joining back the club, then i am in total support of his actions because many players will do the same even though they haven’t paid much loyalty to this team as Messi already did for them.