It's ridiculous, but I can understand if reputation was involved--if only slightly. It's like if Chris Brown's music got banned nationwide after he beat up Rihanna, and the ban remains even after it all blew over. Japan is odd that way like what Crimson Penguin pointed out, but whatever, they're that kind of people.
Still, the short has been around for a little over ten years now, so it really shouldn't matter by this point. She made a mistake and fessed up to it, let it go. The Sakai now is different from the Sakai in 2009, who is different from the Sakai in 2000/2001. I can understand if it was a bigger crime, but she took drugs, she didn't commit murder. And it's not like the little kids are going to realize this every time they watch the short unless they were told about it that very day... which sounds plausible the more I think about it.