It is also true that Blacks do in fact quit the industry at high rates due to bias treatment; based on the number of computer science and technology degrees granted to blacks, their representation should be higher if there was higher retention.
It is also the case that blacks in technology often end in up in specific sectors of the industry, for instance you'll find much higher black representation in the public sector, specifically in the federal government...unfortunately that is not likely to be the source of the next great tech innovator.