Uh, they do. https://abc7.com/irvine-arrests-fbi-raid-molotov-cocktail/13381742/

https://www.cnn.com/2023/06/17/us/east-lansing-michigan-antisemitic-threats-arrest/index.html

https://www.nbcwashington.com/news/local/fbi-arrests-2-in-racially-motivated-plot-to-attack-baltimore-power-grid/3272309/

There’s plenty of garbage law enforcement agencies, but in general the fbi seems to do a pretty reasonable job.