Obligatory Sold a Story podcast link.
I can't help but feel that a lot of this is deliberate, the end result of decades of dismantling the public education system to further divide kids into the upper class in private schools, religious fundamentalists in home schooling, and everyone else abandoned to keep the population uneducated and in worse economic precarity.
Somebody please tell me that the kids are alright 
Certainly possible. But I don't think social media is degrading that comprehension any more than the newspapers degraded it a century ago.
Just like any language skill, its a learned affectation. You're still more literate for knowing it than not.