For players like Lionel Messi, money is no longer the main goal in playing football. It's true he's won everything in Europe, including money. All the luxuries he has are the result of his hard work as a soccer player. An offer from the Arab League is difficult for anyone to refuse, Ronaldo, who wants to continue his career in Europe to be able to play again in the UCL, cannot refuse a large salary offer from the Arab League.
Messi current situation makes it very possible for him to survive on the European stage, apart from Barcelona who still really want his services, Manchester City are also trying to persuade Messi to land at the Etihad stadium. I think Messi will continue to play in European competition even though the salary received is smaller than that offered in the Arab League, because the level of European competition is far above Asian competition.
When he was younger I would agree that money wasn't the main focus because at that time his development would also matter to him but now that age is growingly become a setback it is understandable to seek a huge pay with less hard work, he has established himself and has a reputable career so I think it is time to sit and enjoy retirement.