I am no expert but could it be to do with size/density of text layout, ie physical eye maturity making it harder work?
That said I will confess to reading absolute mush for the most part. I want to read, so I do read, but given I am reading for pleasure/relaxation I read what is easy and convenient. I am so sleep deprived at the moment I just don't have the energy for the denser richer texts that I am well capable of. Maybe like me he just wants a fun relaxing ready and reading something easy and fun is his relaxation?
