I don't think I'm a defender of those in charge but I'll take a stab.
The failure to land a bullpen arm reflects the availability of, or lack there of, relievers that would be an upgrade, let alone significant upgrade, over what Houston already has. Lidge has struggled this season. Was their a dominant closer available that could be had for anyone other than Berkman or Oswalt? So, unless you think Rheal Cormier, Gary Majewski, or DL Guardado would have made a difference over the past 3 weeks, the answer is somewhat self evident.
(edited to revise my ramblings)
Not to mention, Houston did not have any prospects not named Hunter Pence, Hirsh, or Albers that any other team was interested in.