Wasn't there a rockslide that closed it before like within past 5 years or so? 
There have been a number of closings since it opened.  The design engineers fought the route as they knew of some of the challenges to begin with but the politicians won.  Only during the consruction did the engineers realize it was much worse than they thought and have had to come up with new ways to stabilize the ground.  If the engineers knew then what they know now, they would have refused to allow the road to go through the area as too risky, not maintainable.
It was the number of rock slides in the gorge that made the extension of I26 to I40 a much higher priority so there is a "reasonable" alternate interstate route when they have to close it.