> The Google trends for "black lives matter" searches peak in 2016 and 2020. The media only brings it up in election years, even though police brutality happens every year.

That's correlation, not causation. Even if there's a connection to election years, the causality could very well be reversed (e.g. activists increase their efforts to get attention when it matters most). However, I'm inclined to think your observation is just coincidence or misses a critical factor.