You think Tom Brady is poor?
Tom Brady doesn't play for the money. He'd probably pay to keep playing. He's always wanted to play until he was at least 45 years old. He plays for the love of the game, even at the expense of other parts of his life.
The comparison here would be if Brady went to play in NFL Europe or a semipro league for more money. No way, Brady would play in the NFL, even for less money.
[Remember, the main reason Brady won so many Super Bowls is he would always take way less money than he could and renegotiate his compensation.
From what I understand, Ronaldo is still good enough to play in top European leagues, or at least MLS. He's taking more money to play in a vastly inferior league. Can you really see Brady do that?