Is size a confounding variable here? My guess is smaller tech companies with less competitive salaries and narrower recruiting pipelines (and therefor more difficulty hiring underrepresented groups) would be more likely to make this pledge, whereas larger companies would have more trouble getting the pledge through legal and PR departments.

edit: I notice this study was conducted on 240 of the "most prominent" tech companies, not sure if that implies that they are of similar size though.

I'm not sure if meaningful correlations can be made here. The percentage of Black employees could vary due to loads of factors.

Geography: companies in areas with higher Black populations likely have more Black employees than those in areas with lower Black populations, with all other factors equal.

Line of business: "Tech company" is a very, very broad category. Plenty of tech companies have majority non-tech employees. Amazon has much higher overall representation of Black employees, though it (in)famously does not break down representation by role.

I mean I'd hope they employ the best candidate and don't discriminate against anyone. It's not a box ticking game...

Companies particularly vulnerable to political attack end up making these sort of donations in an effort to protect themselves.