I may be speaking out of my ass here, but this is how I see the sequence of events thus far...
J.K. Rowling makes Harry Potter franchise. Its hugely successful, but shes done with it, and moves on to other things.
She releases a book under the pseudonym Robert Galbrait, but its leaked that its actually her before release. The book doesnt do brilliantly, and she gets worried that shes lost the golden goose.
The group she released the franchise rights to have decided to use them. Rowling panics and jumps on board.
...Maybe cynical of me, but it seems like until her new book flopped, she wanted no part of anything Potter related in the future, but now shes on board with whatever as long as it pays.