It's because they're still stuck in the past.
One of the worst things the American public school system did that nobody talks about is romanticize the activism of the 1960s & 70s to the point of mythologizing it. There was an embarrassing amount of time spent on it because the Boomers were so proud of themselves for all of their marching and sign-waving. They've spent their entire adult lives equating their brand of activism with bravery and virtue, and putting into the heads of children that they can accomplish anything by emulating it.
The thing is that it doesn't work anymore. The Boomer concept of activism has been thoroughly cooped by political and corporate interests, and the only time you'll ever see that shit happen on a big enough scale to notice is because it's useful to some institution's goals. Anything that isn't will be ridiculed and demonized out of existence. Any sort of activism that isn't controlled is done purely for narcissism.
But the left doesn't want to realize this. They still want to live in a world where writing clever one-liners on a sign and singing along to faggy folk songs will change the world and put them in history books and documentaries, just like it did before.
It's the same reason they can't see the utterly dire situation Canada and Europe are in right now. They still think the smug liberal comedian bullshit from 90s & 00s is still relevant, so they can't imagine a world where the not-Americans are the smarter, nicer people who do everything better than America.
