It doesn't astonish me. If Rich Johnston is to be believed, and I think he is, they had some version of this story planned for 2020 and decided to bump it until Wanda's show was over. And until then they just didn't bother about her.
"Darkhold" was just a piece of disposable content that (as originally planned) would have come out before her show, and now will come out before her next movie. But they didn't want to put her back on the Avengers, and the needs of the X-Men line have priority in the Cebulski era, so they just kept her on ice until they could do this thing... though this may not be the form it was originally intended to take.