I think you guys are mistaken, Gentrification is not occurring in Brentwood.
The residential neighbourhood surrounding Brentwood was always distinctly lower middle-class, and urban decay, unless you count a SEARS

, was not the case here. Brentwood is simply urbanizing appropriate to increased residential demand along a transit node.
Perception of criminal activity increases with more activity. It's the same reason why the nimby's call out the crime skytrain.