The reason is that cops dramatically reduced the amount of traffic enforcement they engaged in ( https://twitter.com/hknightsf/status/1537100042623848448?t=7... ). Turns out they don't want to risk a murder charge for $65k/year; I don't blame them, I wouldn't do it for $1m. Less traffic cops = more traffic crime.
Both of the dramatic increases of car accidents from the past decade coincided with BLM events: Ferguson and Floyd. See figure 1 - https://crashstats.nhtsa.dot.gov/Api/Public/ViewPublication/...