Any idea why the Art Of book keeps getting delayed?

Back when it was first announced I pre-ordered the Art of Star Wars Outlaws book. It was supposed to come out early June, then got pushed to late June, then again to early July, and this morning I got an email saying it has been pushed to late July. Is that normal? My guess is they've just chosen to add more to it. I don't remember the Art of Jedi books being delayed except maybe once.