I don't know the details well enough, but I do know that there is an effective anti-fedaralist force in the US wherever federal funding is concerned, as it comes with rules conditions (rules) attached. I would be interested to what extent this acts as a bias toward cooperation in the case of ez pass, given the interstate system.
California has a frustrating tendency invent its own systems that are neither better nor worse, but nonetheless incompatible with more widely accepted standards. The highway transponder example actually applies again - Fastrak.
CA has some great ideas too, don't get me wrong (ubiquitous painted curbs: great!) but a lot of the time it's just different for the sake of being different.