I'm not persuaded by some of the ideas they have (like adding diversity to their governing board, seems designed to be exclusive to tech-startups that already have a bias toward that "value"). But if only by competition they make listing cheaper and easier it could have a big impact.
I do not think the bias which you think exists is reflected by the actual makeup of the boards of these tech companies, i.e., who is actually on them.
Also in the end when you mention diversity you end up talking about quotas, because that's the most visible application of it. California already has already set board quotas for women, thus showing you that california companies are by law already "diverse".
[1] https://www.ft.com/content/cdb790f8-c33d-11e4-ac3d-00144feab...
Also there is a body of research that says open offices suck: doesn't mean it has to be a company governing concept.
What on Earth does this mean?
Most speeches about "diversity" are mostly quota-related and, as another comment said, imply is a good on its own: thus not a value.
I have plenty of other opinions about using diversity as a value, but what you can see objectively is that if you grabbed 100 companies that are sensitive to that language, most will be tech. Thus, the selection is gravitating.