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.
Check this:
https://www.forbes.com/sites/kurtbadenhausen/2012/11/30/david-beckham-departs-mls-after-earning-255-million/?sh=42dce3794da5David Beckham got the best possible deal and as per Forbes he earned $255 million while playing for the Los Angeles Galaxy (and that was one decade ago, when the USD had more value). The initial deal was worth $32.5 million in 5 years, but stock option clause made him insanely rich. But the case with Ronaldo is different. He is part of the Saudi bidding team for the 2030 FIFA World Cup and has already taken up residence in Saudi Arabia along with his partner Georgina Rodríguez. And there are rumors that he may go for the Saudi citizenship soon.