The concrete reason to do this is to make life easier for those who are the targets of bias. The hope is that reducing bias will reduce underrepresentation naturally.
There are many conversations about diversity that stray into controversial territory. People start talking about quotas, which leads to arguments about reverse discrimination and the true meaning of a meritocracy. This is not one of those conversations!
I see no evidence that the author is getting anywhere close to suggesting that equal representation is more important than evaluating people based on merit alone. She's saying that most of us carry biases around, and that it's important that we do our best to prevent them from making life and work shitty for our peers.
There's a difference between wanting equal representation "by any means" and wanting it "the right way". This article is advocating the latter--and even then only as a secondary goal--the primary goal is to make sure we don't let our biases create hostility toward those who've already proven they have a right to be here.
(ETA: who is being underrepresented.)
There's (1) symptom/diagnosis distinction (sure, treating the disease eventually cures the symptoms, but we're evaluating it against associated causality and prognosis concepts) and (2) a matter of ethical structure (i.e. deontology vs. consequentialism).
#1 is why they should be separated in theoretical terms. #2 is why they're distinct political programs.
One is bias: take, for example, the archetypal example of orchestra musicians sampling their work behind a curtain so directors can be less unfair when hiring: gender distributions have indeed significantly shifted, because we've removed gender out of view for a critical moment. This, of course, doesn't work if said director is a raging misogynist who will scream "no! no women!" when the curtain reveals the looks of whom he had approved.
The other is underrepresentation. This takes as a given that {women, racial minorities, the mentally ill...} should be represented in important positions in rough proportion to their general share of the population. Now, there are reasons to support this in some cases: preventing that injustices from one generation pass on to the next, for example, or ensuring that the unique contribution that epileptic cyclops can give to the world of cinema. But:
-- not everyone that's in opposition to bias is also in opposition to underrepresentation per se. It's just dishonest to mix the two; particularly in tech circles that have had a long, there's-one-right-answer culture that might not be perceived as benefiting from increased diversity at all. There's also the wider issue of whether diversity should be means to an end or an end unto itself.
(I mean, these are positions that exist. What bothers me is the Trojan horse mechanics at play; it predisposes me against one side when I really haven't thought enough about the subject to have a proper opinion.)