My own belief? There is a new person in charge of the park who doesn't understand athletic endeavors and is trying to push her own agenda. Either that or she can't stand the RD, Chris Kostman.
Using the "extra traffic" excuse is laughable, at best. Suppose in a race like Badwater, where you have 90 participants (and crew). Even if every runner brought 2 cars, you'd still only be talking about an extra 180 cars on the road over the course of 90 miles (I believe it's about this far actually in the actual park itself).
Every runner and their crew leader at BW is required to attend a pre-race meeting where traffic rules are fully discussed and usually there is a CHP officer there, as well.
As we have seen on numerous occasions, if something gets enough negative publicity about a rule or policy change, it usually gets reverted. Is this enough to keep 2014 Badwater held in DVNP? Probably not, but I'd bet the "safety review" somehow gets wrapped up well before the estimated completion date and the events return for 2015.
I suppose that the local businesses from Inyo County could come together and take it to court claiming economic hardship due to an unwarranted policy change. Fighting the federal government is usually a losing battle, but it can be done.