If you want to argue that this kind of violence affects certain races more, that's fine. But why downplay the fact that it affects all races? The percentages are higher for Black Americans, but White Americans still make up the majority of people shot by police[1]. If people actually cared about creating a broad coalition to address this, they would want to highlight both facts, not hide the latter fact.
You actually see the a similar attitude when racists attack social programs. If members of a minority group are more likely to benefit from a program, they treat it as a program for minorities, even if the majority of beneficiaries are non-minorities.
It's also interesting to see how people divide the demographic information. If you look at the breakdown by sex, you'll find that the divide between men and women when when it comes to these shootings is much, much greater than the divide between races. Yet the latter is talked about a lot all over the media, and while I don't think I've ever seen the latter treated as an issue. My guess is that we'd also see another large divide if we divided the numbers by wealth (and this article is a good example of that).
[1] https://www.washingtonpost.com/graphics/investigations/polic...