When my child was ready to read chapter books, he refused to pick them up because he was scared by a lot of black and white text and worried that things would be too hard for him because he only wanted to attempt easy things. I got him an e-reader and the e-book of the book that he refused to read because it had "too much text" on it. I taught him to increase the font size so large that each page had only a few lines of text. And that gave him the initial confidence to attempt chapter books. He raced through the whole series on his ebook reader using big fonts. After that experience, he has been reading mostly regular books because he no longer thinks that chapter books are intimidating. So, it could be that your son has a mental block to "too much text" in a page.
