Because most of what Rosenthal, Olney, Heyman, Gammons etc. report leading up to the trade deadline and during the free agency period is a part of the negotiation tactics the agents use. Sometimes the insiders realize they're being played as pawns and sometimes team execs or agents float things out there just to see reactions, like Boras' "mystery team" thing he does for every big free agent.
The best way to figure out where a guy is likely to go is to take a look at a GM's track record in how he likes to put together his team and what a team's particular needs are. I don't see the Sox getting a Sabathia, Sheets or Peavy despite what reports come out cause they have 3 top of the rotation guys already and Theo has never shown that he likes committing that many years and money to a single pitcher.