"And noting the last few answers why is disproportionate representation of any group in any industry assumed to be always the result of bias, rather than some other reason like the preferences and personal choices of the under-represented group?"
This is a fair point, to be sure, although in some sense answering this question is also a key part of reducing discrimination in all forms. Sticking with gender discrimination: If you have removed, or significantly reduced gender discrimination at interview level and still don't see a corresponding increase in the number of women recruits, then presumably this is because not that many women are applying, so that rather a lot less than 50% of suitable candidates are women. So you can go the next step down, and try to address this instead. If women aren't interested in applying enough, you should find out why. It may be that they don't have the necessary qualifications because they don't take up the subject at school. So you should check why that is too, and see if it isn't possible to redress this balance.
At the end of all this, you usually find that the reason for the imbalance isn't because women just aren't suited by their nature at birth for the job in question, but because some societal pressures or perceptions are driving them away from considering that as an option. Maybe it's seen as a "man's world"; maybe women are actively discouraged not to bother; maybe a lack of role models just hammers home this idea that women aren't welcome, even if this actually isn't true. In the case of certain ethnic minorities, maybe some cultural upbringing drives children in that community in a certain direction in favour of other ones.
Whatever the reason, while any individual person may of course have no interest in one field and that's just a fact, it's extremely unlikely that such preferences will extend across an entire gender, or ethnic background. Skin colour, gender, sexuality, just don't have enough to do with our career choices to have the effect.
It can work in the other way, too, of course. We have just seen the incredible success of the British men's gymnastics team at the recent Olympics. When I was at school, I think you would struggle to find a single boy interested in taking it up. Why? Because they thought it was a thing for girls. Sometimes, it does take seeing people like Max Whitlock, Louis Smith and Nile Wilson demonstrating just how flawed this thought was, on every level, to challenge that perception. And doing so could open up the sport and lead to the next successful generation of gymnasts in 2024.
And not just gymnastics either. Role models can help to challenge outdated ideas about how should do what. We *all* benefit from those challenges, and from trying to overcome the inertia that would otherwise leave these problems. Positive discrimination plays its part in this. Yes, of course we should hope for a time when it's no longer necessary to target a specific minority of the population. Until then, sitting on our hands is many, many times more damaging.