As to why publishing is in decline, I can only surmise. Primarily I think it has more to do with the changing landscape of entertainment. We're awash in a sea of instant, passive entertainment available 24/7.
The issue of people reading less in general is a cultural issue way bigger than anything the publishing industry has done. The effects of book pricing, ebooks and IP management are small potatoes compared to the forces at work beyond their boardrooms. imo.