1. Distractions decrease your ability to think, and the always on media and constant disruptions via texting and pop ups mean that we're constantly distracted. Quality of thought declines, even if intelligence doesn't.
2. Lack of sleep is as bad or worse for judgement as drunkenness. And between late night TV shows and constant media interruptions via texting to assumptions caffeine cures all, active intelligence declines due to lack of sleep.
3. Immigrants who don't have to assimilate bring in a language barrier that makes it hard to work collectively. Collective intelligence and problem solving (per Wisdom of the Crowds) falls because you can't get ideas spread or vetted by debate.
4. By valuing novelty for entertainment and then streaming it, the constant stream of flipping every few seconds between speakers and jokes means you don't spend time thinking about the jokes or plot. It also trains us to get bored if we don't get it fast and tune out, instead of thinking it through.
5. We see problems due to feelings being seen as the arbiter of morality. When we allow the social justice warriors to say "I don't like it, it is hate speech, shut up hater, you're hurting me, say it again and I'll hit you", you destroy dialogue as well as education other than "don't say what offends someone". Ideas are proven when challenged and defended, improved by further testing and validation. When people can live in a thought bubble defended by cry-bullying and violence, you end up with people living with irrational ideas. I've even been told that facts are "hate facts", because the truth is evil because it doesn't fit their narrative, and what they feel to be true trumps what IS true. No one learns or improves that way.
6. To make it worse is their demand to enter conservative groups with a conservative speaker and shout people down if not assault someone altogether (has happened to Ben Shapiro, Milo Yianapolis). When someone's idea of freedom of speech is the demand that you can't speak your ideas even in a room of like minded people, collective intelligence drops because feelings of the most extreme, irrational or insane take precedence.