You sure its not just because the majority who try to ride bikes to the events end up in jail or vehicle-less when the inevitable police blitz happens, with everyone being pulled over 10 times a day anywhere near the event and getting in trouble for even the most ridiculous stuff
you know what, your right, if you try ride your bike to one of these events, the cops see it as a chance to "take you captive', ie: put out a breatho, run some speed camera's every 10km's from the city to the track, set up a defect station, etc, etc....