My guess is that they didn't have the budget to maintain the road, and there may have been a messy recovery of truck from that section that tore things up bad enough that they closed it.I'm not sure the Whale Snot Trail was ever officially a trail. It started as a National Forest road which kept deteriorating as it went along. They only closed that part that was deteriorating. Unfortunately that was the fun part.
Death Valley has considered a different approach to their growing problems related to morons bombing down rough roads. Instead of scrambling to keep the roads in relatively good shape and responding to more and more accidents, they were trying to leave some sections alone so the degradation prevented high speeds and discouraged morons from driving on them at all. I like the idea, and I think other areas will do more planned degradation. Some high traffic trails in Colorado come to mind.