I don't know why you think tech companies would be immune to this kind of thing. I'm not talking about cartoonishly racist people ripping up resumes from black people, I'm talking about unconscious biases that make a recruiter think a white candidate seems like a more polished "better fit" for reasons they can't quite put their finger on. They aren't bad people, this is just a fact of life that we need to actively combat, not ignore.
And like I said, even if Google recruiters are somehow completely free of bias, that doesn't solve the problem. Black people are less likely have the necessary qualifications because of lingering effects of racism in the past, which means they're less likely to get well-paying jobs and move up the socioeconomic ladder, which means their kids are less likely to move up and the cycle continues even if racism completely disappears. Obviously it would be nice if we could solve this problem at the source by making education and childhood development completely independent of socioeconomic background, but that's sort of an impossible ideal. I don't think it's unreasonable for Google to try and address the symptoms when the cause is fairly insurmountable.
And one more thing, you're right that anyone hired by Google has exceptional qualifications, but consider what it takes to get your resume in front of a recruiter. When I applied to Google, it was through a friend who had just been hired giving my name to their recruiter. This clearly gave me an advantage over just uploading my resume to a job site. And during the application process, they asked for the names of anyone I knew currently working at Google so they could ask for recommendations. This is a fine step to have in a recruiting process, but you can see how network effects would continue to affect a group that's been discriminated against in the past, even if they're treated completely equally today. They're less likely to have a direct connection to a recruiter, less likely to have internal recommendations, less likely to get that extra boost.