1. Adults read less, so children see their parents reading less often (it at all!) so do not grow up thinking it is a fun thing to do. I love reading because my parents did, and my kids do because I do.
2. Schools do not make reading enjoyable. A teacher I know suggested that their school did somethings to make reading fun, and the management refused because it improve any of their metrics. A friend of by daughter's went to a school where there were times when they had to sit and read a book - nothing kills enjoyment better than being forced to do something. You are telling kids its a chore you have to do, not something done for fun.
There are other things do. There are schools that teach Shakespeare for English literature GCSE without giving them the whole text, and without watching a video of the play, let along going to the theatre.
3. There are fewer and smaller local libraries so kids cannot discover what they like as easily. There are fewer bookshops too, because people read less.