As Jon Freeman's link states, criminals are deliberately causing accidents by cutting vehicles off and then hitting the brakes. There are numerous videos on YouTube showing this occurring.

This is so stupid that at first I couldn't believe it, but now that I know that gangs are involved, I accept that anything might happen. Maybe I should buy stock in companies that sell dashcams.

Some brake checking occurs because of tailgating, but that seems to be unusual. Most people are too smart to stomp on the brakes when there's a vehicle close behind. Besides, Archie Goodwin, Nero Wolfe's assistant, taught us that we can spook a tailgater by turning our lights on and off, which creates the impression that we braked, even though we did not.