Carnivore diversity was much higher in the Late Pliocene -- which means more frequent and varied scavenging opportunities.

There might have been a very small, precious window where early hominins had the chance for this discovery because of abundance.

[1] Origins of the Human Predatory Pattern: The Transition to Large-Animal Exploitation by Early Hominins: https://www.journals.uchicago.edu/doi/abs/10.1086/701477?jou...