Old super star players have a high ego, no one will admit if their performance are declining due to get older and keep demanding high salary. There's no league willing to pay high salary for a popular player without good performance except Saudi Professional League.
So their options are either retire or joining Saudi Arabia, this can't be denied.
This is not entirely true. Name me at least one football player who has a higher ego than Ibrahimovic? But at the same time, in recent years in Milan, he played for a symbolic salary. Everything is individual, plus we should not forget that the salary is made up not only of sports components, but also of media ones. For example, Ronaldo will get a big salary everywhere (at any age) simply because he is a super brand and #1 in Instagram followers.