I thought that Modric would either decide to end his career or go to Saudi Arabia or MLS. But his choice probably surprised many fans, he decided to continue playing in Europe. I think the reason was that he feels that he still has the strength to continue playing, but at the same time he already sees that he spends too much time on the Real Madrid bench, and this does not suit him, because he does not have much time left when he will have to end his career as a player. In Milan, he will have a place on the field, I think this is another reason.
His age was the major issue with Real Madrid, the club is a competitive club and this too doesn't sit well with their philosophy. A competing club like Real Madrid doesn't keep old legs for long at the club. But left to him alone he still wants to play and would have still been at the club and retire there.