I am skeptical that this "deep literacy" is in fact eroding, since it's what lets you learn a topic well enough to get a degree. It's also hard work; I'll put in the effort on topics that matter -- as in topics that usefully inform my future actions, rather than topics that have abstract moral weight or whatever -- or sometimes for entertainment, but it's not a casual "all the time" thing and there seems to be a limit to how much I can do in a given day.
I learned growing up that TV rots your brain. Modern social media works the same way, except that sometimes you can actually engage with it and maybe it rots your brain a bit less in that case. This is called "mindless entertainment", and various forms of it have always been fairly popular. When I use shallow reading for mindless entertainment, it displaces whatever else I'd be doing for mindless entertainment. Which is different from displacing serious reading, or even from displacing learning things for entertainment / mental exercise.