Now imagine you're the same kid watching a movie in a theater and everyone else is silently watching, too. You're so enhanced by the plot you hardly notice the smell of popcorn.
That's like the difference between being a good reader and an excellent one.
Kids may be able to comfortably read and understand everything required to get good grades in school, but if they don't read for pleasure they probably aren't excellent readers.
Excellent readers get carried away into fictional worlds and tune out everything going on around them.
Of course there are things like learning disabilities, learning to read in a second language, or vision problems that make reading difficult but lots of kids who could be excellent readers aren't because they've never experienced the joy of getting lost in a book. If other people in their family only read for information and the kids think of reading as a task they won't learn to love it.
It can help kids become excellent readers to read to them a lot when they're young, let them see their parents read for pleasure instead of watching TV, and have books they're likely to enjoy available. The reading levels of the books should neither be too difficult, nor easy enough to be boring.
Then when the kids have become good readers they should be encouraged, but not required, to read for an extended period without interruptions or background noise. That way they might experience what it's like to get carried into another world. If they experience it even once, the kids will probably want to do it again and again and they'll be excellent readers..