When big firms drive industry consolidation in a business with high (capital, name recognition, breadth of facilities) barriers to entry, they can achieve pricing power. Thank you, EnterNatAmo and AviBud.

Some fleet size reduction may have been sought by agencies themselves in response to the travel downturn, some forced on them by GM/Chrysler bankruptcies (and extensive production shutdowns that yielded zero fleet sales during those shutdowns - nationwide fleet sales don't come from dealer inventory), and some by reductions in credit available to the car agencies. No matter the cause, open market rates can be high in some places and dates.