My best guess is his contract scares teams. Let's face it, there are only about 8-10 teams that can even consider adding bigger contracts. Most smaller market teams are going by the way of the Rays and A's. Draft, develop keep cheap talent OR add middle range guys who aren't stars but are servicable major leaguers. I look at a team like the A's for instance, Jed Lowery, Elvis Andrews, Tony Kemp, Starling Marte, Josh Harrison, Yon Gomes...major leaguers who are solid but not all star type players, good team friendly contracts. They sprinkle in their own young guys who are on their rookie deals and they stay competitive.
I just don't think you're going to get alot of trade talks with Geno. Also working against him is his HR numbers are inflated in playing at GABP. In my mind, that's a reason to keep him. Even in a perceived awful year like this year, he's in the top 25 in the NL in home runs and the top 30 in RBI. And pretty much the last month his playing time has been cut down significantly.