it's kinda weird and rude of you to assume everyone has the same exact life and participates in the same exact activities and communities as you.
teachers don't outright say the n word in history class, and there are some schools that don't teach about it at all. not to mention how there are countries other than the us where people don't really care or bother themselves with that stuff at all.
the blm trend was mainly a twitter thing. it wasn't as widespread as you think it was, and a lot of people just stay out of the loop. also, once again, it wasn't a worldwide event.
pewdiepie saying a slur was a very minor and unremarkable situation outside of some youtube communities. news about it were trending for less than a week and it's not unlikely op simply missed the whole ordeal.
and nobody ever watched politicians on tv. that's the most boring way anyone can spend their time.
everyone learns some common knowledge things differently, so there's no reason to blame someone for not knowing what you think is obvious. it's likely op learned that the n slur was just a curse word and nothing significant.