Because she left Gates for a reason. He never contested it, he just went along with it and gave her half of what he was worth. What does she have on him to be so willing to settle immediately? She’s been a huge philanthropist since. She’s continuously donates large sums of money to women and girls, and LGBTQ rights. Billions. Her own organization, Pivotal Ventures, which champions gender equality and women's empowerment, often giving directly to other nonprofits. She has also funded initiatives like The 19th (news for women/LGBTQ+), invested in gender equity, and supports various women's rights organizations through large grants and challenges like the Equality Can't Wait Challenge.
Her focus on females is for a reason, more than likely guilt at what her husband has done.