I think a lot of it is that they are a segment of the population that just likes the feeling of being "heard". They like the attention for lack of a better phrase. I think growing up on social media influenced that.
It's all anecdotal, but I always hear and see them reference "being a part of history." I think it started with the election of Obama and continued to things like the gay marriage ruling, BLM protests, etc. They're hooked on that feeling. It's backed up by an education system that semi-worships protest movements in many history classes.
I'm still building my thoughts around it but that's where I'm at. When you talk to them, a huge part have an incredibly shallow knowledge of what's going on. There are some that go beyond an emotional level, but they seem few and far between.