Why offer our third (or fourth depending on how you evaluate) best prospect, and at a position we don't have a surplus of, for a very good player that the Padres MAY not have that strong a market for?
Before they collapsed I would have thought that the Phillies were the team that needed him the most and would pay a premium by the deadline, but they look to be sellers now. They might be interested again this Winter, but there's no guarantee.
Let's look at whivh teams NEED a 3B.
Boston - NOPE, they are happy with Middlebrooks.
Yankees - NOPE, Arod.
Tampa - Nope, Longoria.
Toronto - NOPE, just extended Encarnacion.
White Sox - Probably not. They'll give strong consideration to bringing back Youkilis.
Detroit - NOPE, Cabrera.
Cleveland - Maybe, but they have other holes to fill so they probably won't be willing to pay a premium for Headley.
KC - NOPE, Moustakas.
Minnesota - Maybe, but they have Trevor Plouffe that can play there and they also have too many holes to pay a premium for a position they can fill from within.
Angels - Maybe, but their farm system is almost dry and they have Callaspo to play there.
Oakland - Probably, but they're a team that looks for a bargain so I doubt they are willing to outbid anyone for a player. They also have Stephen Parker at AAA that they might want to give a chance before they "outsource".
Seattle - NOPE, they'll give Kyle Seeger a chance to show whether he should keep the job.
Atlanta - Maybe, because Chipper will retire, but they my want to allow Juan Fransico to earn the job.
Miami - NOPE, Ramirez.
Mets - NOPE, Wright.
Washington - NOPE, Zimmerman.
Cubs - Maybe, but they might allow Josh Vitters to show whether he's a ML player.
Reds - NOPE, Rolen's at the end of his string but Todd Frazier has been a solid player at 3B and will probably go into ST with job as his to lose.
Houston - NOPE, they have Chris Johnson and won't be paying a premium for any player while they're rebuilding.
Milwaukee - NOPE, Aramis Ramirez.
Pirates - NOPE, Pedro Alvarez.
Cards - NOPE, Freese.
Dodgers - Now THIS is a team that will need a 3B and don't have a ready prospect in their system; however, San Diego would probably prefer to trade outside of their division and league if they thought the offers were roughly the same.
Giants - Nope, Sandoval.
Arizona - This is a team that will need to find a 3B, but they may give Matt Davidson a shot in ST. AND they probably won't want to pay a premium to block Davidson if he's not ready in the Spring, AND San Diego would probably prefer to trade outside of their division and league if they thought the offers were roughly the same.
Colorado - Also a team that needs a 3B, but they have some in house solutions for 2013 and probably won't want to pay a premium to block Nolan Arenado who may be ML ready in mid 2013, AND San Diego would probably prefer to trade outside of their division and league if they thought the offers were roughly the same.
There's one more thing to consider: the Padres almost HAVE to trade Headley this Winter to open a spot for Jedd Gyorko. If they keep Headley once Gyorko takes over 3B they will have to move Headley to the OF where his trade value will be reduced by at least half. San Diego isn't going to GIVE Headley away but, IMO; an offer of Matusz, Hoes or Bridwell, and a lesser prospect MAY get this deal done now as the Padres MAY not get a better offer and they know it.
Not that Toronto needs a 3B but Encarnacion is a nightmare defensively. Lawrie is locking down 3B in Toronto for the next 10+ years.