I have to think the PED suspension helped tip the balance. They just weren't as invested him as they might have been had the major league coaching staff been able to work with him during that time, it was basically like giving up on him in April. And they had to churn through so many relief pitchers, the ones who couldn't be sent down were tough to hold onto even w/o Rule V (Oberholtzer, Bailey). I know Oberholtzer appears to be toast, but even he wouldn't have been bad to keep.
They sure didn't like any of the lefty relievers this year huh? Russell never got another look, Araujo couldn't stick. Rodriguez ended up getting the last look over all of 'em.