Quality of what's produced in that medium might be one thing. People reading for pleasure are usually reading works published by authors that have gone through some sort of filtering process for quality. Sure, it might be "trashy" novels relative to literature, but at least there's a floor to the quality level or else it just doesn't get published.

But with the advent of other forms of media, more easily produced and consumed, the quality of what is being consumed is lower than the quality of pleasure reading. Combine that with the firehose rate at which it's being consumed and pleasure reading seems better than it might once have.

Similarly, I listen to a lot of podcasts, but whenever I listen to The Guardian Long Reads (read articles) I’m kinda surprised every time how much higher quality they are than typical podcasts, since they’re based on well written articles.