Lionel Messi can still play at the top of the competition without any hesitation. So it is probably not going to be the best idea for him to move to a league that is not that competitive. I believe after all it comes down to him thinking that he has done everything that there is to be done in football. So he is trying to chill right now. Might also be him losing the competitive mindset.
Honestly tell me what more can he achieve in his career? I do not think there is any motivation for him as well. The only thing that he was missing from his career was the world cup. And, now he has that as well.