It's an ongoing debate:
> In a wide-ranging review published in February’s issue of Current Anthropology, Thompson joins a team of researchers to weave together several strands of recent evidence and propose a new theory about the transition to large animal consumption by our ancestors. The prevailing view, supported by a confluence of fossil evidence from sites in Ethiopia, is that the emergence of flaked tool use and meat consumption led to the cerebral expansion that kickstarted human evolution more than 2 million years ago. Thompson and her colleagues disagree: Rather than using sharpened stones to hunt and scrape meat from animals, they suggest, earlier hominins may have first bashed bones to harvest fatty nutrients from marrow and brains.
> Then, starting in the mid-1980s, an opposing theory arose in which Homo’s emergence wasn’t so tightly coupled with the origins of hunting and predatory dominance. Rather, early hominins first accessed brain-feeding nutrients through scavenging large animal carcasses. The debate has rolled on through the decades, with evidence for the scavenging theory gradually building.
> Because large animals such as antelope pack a serious micro-and-macro-nutrient punch, scientists have thought their meat contributed to humanity’s outsized brains. A consensus arose in the 1950s that our ancestors first hunted small animals before moving on to larger beasts around 2.6 million years ago. Flaked tool use and meat eating became defining characteristics of the Homo genus.
You know, "science advances one funeral at a time" and all that.
Plus, I'm sure there is some kind of power-fantasy attachment to the older theory that basically puts humans on top of the food chain as apex predators due to our intelligence.