Question number 71-73 are based on the following passage.
 

    The animal bones [found in a region of Africa by the anthropologists] exhibit numerous cutmarks, and they were often broken for the extraction of marrow. The implication is that the Klasies people consumed a wide range of game, from small, greyhound-size antelope like the Cape grysbok to more imposing quarry like buffalo and eland, as well as seals and penguins. The number and location of stone tool cutmarks and the rarity of carnivore tooth marks indicate that the people were not restricted to scavenging from lions or hyenas, and they often gained first access to the intact carcasses of even large mammals like buffalo and eland.

    But the bones also show that the people tended to avoid confrontations with the more common-and more dangerous-buffalo to pursue a more docile but less common antelope, the eland. Both buffalo and eland are very large animals, but buffalo stand and resist potential predators, while eland panic and flee at signs of danger. The Klasies people did hunt buffalo, and a broken tip from a stone point is still imbedded in a neck vertebra of an extinct "giant" long-horned buffalo. The people focused, however, on the less threatening young or old members in buffalo herds.

    The stone points found at Klasies could have been used to arm thrusting spears, but there is nothing to suggest that the people had projectiles that could be launched from a distance, and they may thus have limited their personal risk by concentrating on eland herds that could be chased to exhaustion or driven into traps. The numerous eland bones in the Klasies layers represent roughly the same proportion of prime-age adults that would occur in a living herd. This pattern suggests the animals were not victims of accidents or endemic diseases, which tend to selectively remove the very young and the old, but rather that they suffered a catastrophe that affected individuals of all ages equally. The deposits preserve no evidence of a great flood, volcanic eruption, or epidemic disease, and from an eland perspective, the catastrophe was probably the humanability to drive whole herds over nearby cliffs.

According to the author's theory, why did the Klasies people focus on eland instead of buffalo?