Your entire point is predicated on the assumption we don't, and so your whole argument falls.
For example, what's unfalsifiable about "evidence shows racism and sexism is still rampant in executive appointments". It's verifiable and falsifiable. You can, in less than a minute with a search engine, find the percentages of women on executive boards.
You can verify the representations are not proportionate. There is no evidence that, if no oppression existed, the representations would be proportionate. This is a very basic and clear difference.
The NBA has a very high representation of black men, and a very low representation of Jewish or Hispanic men. This in no way proves racism is rampant in the NBA. The cause is likely other factors, and if you decided to "positively discriminate" against black men to "fix" this problem, you wouldn't actually be "fixing" anything. You'd just be rationalizing discriminating on a racial basis.
The reality is that you can draw lines anywhere between large groups of people and see different outcomes. You will see different outcomes between people born in New York or LA. People with brown eyes and people with hazel eyes. People in Kansas and people in Arkansas. We can openly acknowledge differences in outcomes between these groups will happen despite a lack of systemic oppression keeping one or the other down, yet as soon as race or gender come up, people insist we have to put blinders on and pretend we're all identical robots all the way up into the board room / Congress.
When you outright assume that differences in outcomes are caused by oppression, you're making an unfalsifiable claim. Nothing has been proven, and you could just be wrong. And if you're wrong, then you're just rationalizing racism against people you perceive are unfairly oppressive. But since it's unfalsifiable, you can never be called out on it.