Alexx that EZ Pass system is not unlike the Austrian Go Box System. Gernany decided not to go with that sort of system as it would have required a lot more construction of readers on every junction in the Autobahn system to log when a vehicle left or entered the network. There would still need to be an alternative for those that did not have an OBU fitted which would either have been Toll Barriers with personnel to collect the toll via cash or credit card or machines were it would need to be booked in advance, much as they now have. The OBU is only another variation on the EZ Pass type system but instead of passing under a reader it is done by GPS. There are 300 ‘MAUT Brucke’ on the network but they are to be used for enforcement rather than billing.
There are a vast number of exits on the autobahn network and to put Toll Stations on them all would have been a massive undertaking, even needing the redesign of the exits in most cases. In France for instance whichever side of the Autoroute you exit from the road is designed so that you all pass through the same Peage barrier, German Autobahn exits are not designed in that way so it would have needed even more barriers or a reworking of the junction.
The other option would be, like the Austrian system to have a reader just after every junction and your vehicle is monitored as it passes along the network, if you are clocked on one reader but not the next you must have taken the exit. This would still have needed a vast number of gantries over the roads.