Kids aren't reading because adults aren't reading. Parents might say "you have to read because it's good" but then they don't do anything to facilitate a love of reading.

Different things are contributing to this, but I think technology is the main culprit. And not so much in an "it makes kids too stupid to read!" sense (though I have my concerns about tech addiction and how it might damage the attention span) but in the sense that it competes for their time. Any time you introduce a Cool New Thing, that's going to mean less time for the old things. These days it's normal for teens and even preteens to have smartphones, books have a hard time competing with that.

I'm also thinking that it's a problem that perpetuates itself. Like, they're reading less as preteens, which means that they aren't developing reading skills as well as they otherwise could. This causes them to read less and less over time, because reading is boring when it's too difficult.