Over at Human Transit, Jarrett has an excellent post detailing why dedicated park & ride facilities (as opposed to shared use of existing parking lots that have another principal function – like church lots) make no sense from either a transportation or land use point of view, especially when there is no charge for parking. We see this absurdity locally, with TriMet charging for card-lock cage bike parking, but allowing autos free parking. (My beef is NOT with charging for bikes, it’s with the free auto parking!)
Historically I think we owe this pattern of development to a degree to the Federal Transit Administration. They used to grade New Starts applications on a metric called TSUB (Transportation System User Benefit) which was essentially a score for how many people you move how far, how quickly. In that formula, boarding a lot of riders from park & rides probably gave you a boost in a score, at least in the early years of operation of your corridor (before TOD built out).