I’m not sure I agree this is making a difference in the recent downturn in literacy scores dating to around 2012. The books available in the drug stores, airports, and grocery stores have been the trash mass appeal types since I remember, but the publishers are still publishing plenty of variety and even if they stopped altogether there are a plethora of interesting books that already exist across the spectrum. I don’t think it makes sense for this to factor significantly into recent shifts.

The decline in bookstores seems a more reasonable guess since that cut off an access point for browsing a good variety. Maybe also the decline of mall culture which probably brought more casual browsers into bookstores than a standalone barnes and noble in a strip mall does.

If I were to look for causes explaining a reduced desire to read among kids I would look at whether parents are reading to kids less or maybe less likely to sign them up for library reading programs, whether districts/teachers are offering less variety of book options for their K-8 classes, whether reading programs at schools or libraries are offering less lucrative prizes or generally encouraging it less than they used to.