Because even among those who are looking at abuse and discrimination in our legal system, there seems to be a systematic lack of focus on sexism. Is the reasoning due to a lack of awareness of sexism, which seems unlikely given we are talking about the group that is vigilante of police discrimination. Or is the group itself largely unconcerned and thus showing their own biases.

And I use 'group' loosely since it is really more of a sub-culture than a defined organization.

Look at it this way, a black man that is unjustly shot by police is more likely to be shot because he is a man than because he is black. If we want to stop unjust shootings, we should focus on the factors leading most to them, or which racism is second behind sexism (and maybe third behind classism, though since class is less apparent in short interactions than race and gender, it may end up not being as big an influence until we get to the court room).