5-10 years ago in the grocery store line, myself and half the people in front of me were bringing our own reusable grocery bags. I feel guilty acknowledging this, but we all just seemed to... stop. Because it was a mild hassle, and the novelty wore off. I can't remember the last time I've seen someone with with their own bags, and I imagine that younger store clerks would be confused by them.
We're still concerned about plastic (that worry comes and goes like a pendulum). We just got bored and lost our attention span for one of the most direct things we can do to reduce plastic.
10-15 years ago, myself and most of my political peers were more upset about Guantanamo Bay than plastic or climate change. Nothing ever changed there, but I can't recall the last time I've heard it mentioned. The average anti-war protestor of the post-9/11 years probably understands little to nothing about U.S. action in Syria over the past decade.