Azar hardly played in the last 2-3 years and rested on the bench, only 76 matches in 4 years is nothing, so he should have plenty of strength.
Now he's a free agent, he can go wherever he wants, plus the level of competition with MLS is lower than in La Liga, maybe he can play. Maybe he had a psychological trauma that he could not play, and he can forget about it across the ocean and start with a clean slate, besides, Messi will be there, maybe he can help in some way.
In any case, Azar has a lot of talent and it would be a pity if he completely buries it in the ground.
It's better to let him try, maybe something will work out.
Most likely, it was the injuries that plagued him over the years, he did not even manage to get into optimal shape, and he returned to the infirmary again. Here neither Messi nor anyone else can help him, perhaps after so many years he himself does not believe that something can change. If you try to play more carefully, then it won't work out either, in order to score goals, you need to fight in attack with the defenders. MLS is not much easier than La Liga, there is also a very dynamic game and I don't think Hazard will be much easier there than in Real Madrid. But of course he need to try something, just sitting on the bench in Real Madrid is not an option.