If I had to hazard a guess I'd say how everyone has the internet in their pocket, news and entertainment being one and the same, and the fact that nobody reads books anymore
Book sales in general (across all formats) are up I think - so there are still many, many readers around. We just have many new formats (EPUB, audiobooks, reader devices, etc.) and of course population is increasing over the globe. I'm pretty sure we have the highest number of readers on the planet right now than ever before in absolute terms.
I'm not sure that's still correct. There was an uplift because of Covid and people having more spare time, but whatever more recent (2024 - 2025) sources I can find suggest the trend has reversed.
It's worth also considering demographics. If you narrow the focus to just younger generations (who, we can guess, are more addicted to smartphones) then the numbers look pretty bad. E.g.:
My son, who is away at college as a freshman this year, recently phoned me and apologized for calling me a bad dad and thanked me for not allowing him to have any devices in his bedroom after bedtime growing up, as it made him become a reader. He said he was amazed when he got to school and nobody else reads for pleasure.
I can't fault people for feeling that nobody reads anymore. In the US today the majority of Americans can't even understand books written at a 6th grade level and literacy has been trending downward. Only a small number of us are propping up book sales.
Audience matters here. Most book sales have been falling. The one increase has been in romance porn with those books accounting for some 50% of all paperbacks sold at this point (they are dominating for the exact same reason porn dominates internet video content).
Personally, I don't count pornhub traffic the same way I count Youtube or Netflix traffic and I think the same applies here.