There's lots of research to answer the question of why the internet is different than books. For one, books take extended periods of concentration to digest while many applications on the internet are being hyperoptimized to give a constant and frequent dopamine drip.

I'd recommend perusing The Shallows by Nicholas Carr, which suggests that exposure to rapid and substance-less feedback cycles can actually change brain chemistry in undesirable ways. The book is a bit sensationalist, but is nonetheless a good jumping-off point for exploring the perils of internet addiction.