Because having women in senior leadership has been proven to impact businesses positively with regards to profitability, social responsibility, health and safety, and customer service. In addition, having women around the decision-making table also reduces excessive risk-taking, while promoting wider change and transformation.
Secondly, research also shows that it is in fact only when there is more than one woman at the leadership table, that there is a substantial and significant shift in thinking and action by the collective.
The reasons for this are not yet conclusive, but the evidence is. I can however comment that, anecdotally, I have heard over and over from the lone woman on the board or executive committee, that her voice was often drowned out. In addition, women report having to provide a substantial amount of evidence, data and vouching for by other credible voices, in order to have their own strategies, ideas or perspectives taken seriously.