The GDP of the 41 Heavily Indebted Poor Countries (567 million people) is less than the wealth of the world’s 7 richest people combined.
Cancelling this debt is therefore “doable”. Cancelling this debt could lead to better lives for many of the 567 million people in those countries (other social changes would be needed to ensure that the cancelation of debt did lead to better lives). Yet it won’t be done. That is why we need to change the world.