That is not a new trend. It is very standard for players who are at the end of their career and want to make big money for a last time. Just see how many players went to China or Japan when they didn't have salary caps. Iniesta plays for Vissel Kobe or Hulk played for Shanghai. Xavi played for al-Sadd for even four years. Nothing new about it and not to forget how many stars went to the MLS. Ibrahimovic, Henry etc. It is all about the money.
Didn't David Beckham also sign for a MLS team? I can't remember which one, but I think it was a team that was playing in the MLS. What I want to say is there is nothing wrong with that. Starts in their "old age" like those you mentioned or Beckham probably won't bring much quality to a club. But they will bring much media attention and money from marketing. Look at Christiano Ronaldo for example. He signed for a club that I never heard of until media started writing about them signing Ronaldo. And they have enough money to pay him much more than he would have earned in Europe.