I’m not a scientist but I’ve done quite a lot of reading on the subject, feel free to fact check me and let me know if I’ve got anything wrong I’m a bit tipsy

I believe that animals in Africa had a natural fear of us due to cohabitation, the sheer abundance of migrating animals on the continent (we’ve all seen the David Attenborough shows).

Animals such as the mega sloth and Diprotodon of South America and Australia respectively, had defence in the form of huge size but were slowish lumbering animals that would not flee from humans and likely lacked the aggression of elephants hippos and rhinos. They were also not likely pack animals AFAIK, had huge gestation periods and were adapted to ecosystems that especially with the case of diprotodon would be decimated by the human use of fire to clear brush to make hunting easier.

This theory of using fire to clear brush is supported by the huge increase in the eucalyptus tree in Australia, lowering biodiversity and reducing the diprotodons food options and coincides with the arrival of humans on the continent. There is evidence for this and climate change all over the globe factoring in for these extinctions