MLS can't offer money like SPL. If Messi's after money he'll sign a mega contract with Al Ahli. He's played in Argentina Spain & America so if he wants new experiences he'll leave Inter Miami. Messi's got options to stay in Inter Miami or go to SPL.
That is why they are not really offering him a "salary", they are offering him a revenue share. Meaning, he gets a cut from the money they made. Also, why would he need a new thing? He is living in one of the best places for an Hispanic person to live, Miami is a great place. As a Christian, it is not easy for someone to decide to go to Saudi league, while we have seen plenty who accepted, we have also seen plenty that rejected.
Most famously, Kroos rejected big time, like literally joked about it. So we are seeing Messi, who already makes 100 million a year, from the revenue share, and saying, he should go there? Why? Miami is better, and he has money, there is really no need for "even more" money, he is not making 5 million and offered 500, he is getting 100 and offered 200+, so it doesn't worth it for him.