They had a bunch of protests during 2020, and a couple of those protests got out of control (Kyle Rittenhouse famously murdered several protesters at one). The conservative news space spent the next 6 months painting them as a Marxist terrorist group and a lot of people bought in to that framing.

I think there were some clashes during the protests and also the movement got kinda perverted into some pseudo racist exclusivity and also had a lot of white people with white saviour complexes. There are also the folks who think that it should say All Lives Matter but they are kinda missing the point.