I have two guesses. First I think YA is very heavily influenced by Vertigo series and they try to cross promote. Like when the Suicide Squad movie came out and they reprinted Bronz and Silver age books for that even though they had very little to do with the movie's story.
Second: I think they realised how under represented or oop most of the books are and graphic novels are a growing market in bookshops and Vertigo in its prime was the series that appealed most to the bookshop crowd, reaching out to general audiences (or at least to the intelligent side of it).