You help out reporters in return for good press
I wrote that in my last sentence.
But: Trading informaton for good publicity is (hopefully) not something a reputable journalist would do. Its extremely unethical and the player in question who could be caught feeding information not intended for the public risks a huge windall that includes the termination of his job contract under the "putting the club in disrespute" clause thats part of the standardized EPl contracts.
"Luke Shaw is ready to sign a new contract" is information that is unproblematic to leak. Its not a negative nor is it sensitive information
"Paul Pogba gets into heated fight with Jesse Lingard in the dressing room" IS information that is harmful and carries pretty significant risk to leak for a player, IF they are discovered. There are probably more than one hand in the relevant news organization that knows who the source for any claim is. I would not want to risk my reputation and career on the safety equalent of "12345" as my password.
But, maybe I am just hopeful and assume that people behave like self preserving adults.