They're stopping them at the level of the words. Yolen isn't the only author who sees the death of literature through basilization. And new educational reforms without supporting intensive staff development may force teachers to either accept district adoptions or dig deeper into their own basilized renditions of popular children's books. Students will get more of the same. My feeling is if you want people to savor a book, you don't want to have to destroy it.
Many people have no idea how to read below the surface.
Literature is infinite, expansive. This question, combined with the fear of low test scores, often drives administrators and teachers to basilization. Some words a child doesn't know that becomes a teachable moment. Reading is supposed to be work, but the payoff is the pleasure of reading. I think the problem is people often use an elephant gun when they're hunting for butterflies.