“I came across this at a very sad point in my life, it was on a hard drive on a vintage computer I bought off Amazon,” Marshall explains on the expansion’s GitHub page. “Literally this essentially saved my life, I was going through a divorce and just happen[ing] to come across something like this was insane.”
He doesn’t hold the copyright so has no right to distribute it. Like if you bought a manuscript from a book you don’t have the right to print copies of it and distribute it. Since you only are the owner of that specific manuscript not the copyright and distribution rights of the actual content.