As far as I can tell it's just that the the approval hasn't been renewed once it expired. If there's no demand for it then there's no point in spending money one something you could plant either way. There was a time where hemp was legal (hemp being cannabis for industrial purposes no matter its THC content) and then there was the time where it wasn't any longer. And then EU varieties became legal (Fédora 17 is one of those) and that's about it.