Many companies have pages on the web explaining why they value diversity. In its most direct form, it comes down to getting input from a much wider range of people than, for example, able-bodied white cis-gender male American college graduates. There have been some fairly spectacular blunders when people didn't understand that there was more than one subculture, and indeed more than one macroculture, in their potential market. Or when AI's were trained on faces in the above mentioned groups and then performed horribly on other populations. Or... it's a long list, actually.
Could they have been aware of these issues and addressed them without a more diverse employee base? Theoretically, yes. In practice, there is more than sufficient evidence that they didn't, or did so poorly. The fact is, we don't always understand the other person's viewpoint as well as we would like to think we do, and that can make a serious difference in success of a campaign or a product.
More viewpoints also tends to yield better creativity and fewer stupid errors.
There is also the simple fact that there are institutionalized biases in many companies, just as there are in society, which need to be fixed entirely as a matter of social justice. You can quibble about the exact mechanisms that would be best for this purpose, but if your staff doesn't statistically resemble the candidate base odds are high that you are doing something you would really rather not be called out for doing.
(In fact, I just had a good example of this. I was one of a bunch of early readers for a short story. Pretty consistently, women understood the author's intent -- that the entire story was an internal monologue by one of the characters, explaining her recent history to herself -- and men did not, interpreting it as third person. Like it or not, culture and experience do affect perceptions, even when we're actively trying to see through another's eyes.)