Unsuprisingly, reading makes you a better reader! Increasing concentration, vocabulary, articulation and general productivity of the mind. This isn't just about reading books. Any type of reading, be it books, magazines, articles, and pretty much any other thing with words on it, can help improve literacy skills. However, there are studies that show most teenagers and kids get their bulk of their reading from tiny snippets of words they find on the internet. While they might read much more than the previous generations in terms of shear magnitude of words, they lack complexity and meaning. The only reading skill that could come out of such is increasing reading speed. Therefore, the problem is that non-adults are starting to read less books and what they do read are starting to become more simplistic.
This isn't a new phenomenon, it's logical that when people grow up, they lose the time and interest in activities they did as a child. However, with the invention of the internet, lack of interest in traditional 'childhood' activites have dropped by unprecedented levels. Internet addition isn't a new thing in the scene either. It isn't that they aren't interest in books either. Among children and older, there is still a minority that are strongly interest in reading traditional books. The problem then comes down to commitment. It's easy for people to start doing something that doesn't interest them and lose interest soon because there is something that is much more fun: the internet. Also, not just the Internet but people have more access to a bigger variety of entertainments. With an decreasing amount of free time and an increasing amount of entertainment choices, reading books tend to get sidelined. Due to these reasons, schools are under pressure to increase the reading skills of their students.
There are many possible side effects of not reading proficiently. One of the more pressing matter is that those who lack certain levels of reading skills consistently land in poverty or the lowest paying jobs. In a evermore increasingly complicating world, people who can only read simpler texts are not beneficial. In order to advance human civilization, there needs to be a comprehensive understanding in the studies people undertake. That obviously cannot happen without good or even excellent reading skills. Finally, and one of the more important matters in the long run, is the lost of knowledge and wisdom held by books. Centuries ago, most books were written with a clear purpose: to pass on knowledge and lessons in whatever shape or form. When reading becomes a endangered activity there is a threat that next generations won't have the chance to grow up with enough morals and ethics these books could possibly teach.