Why do archaeologists think that many people who lived in Mehrgarh were hunters to start with and that herding became more important later?

Archaeologists think that people who lived in Mehrgarh were hunters initially but became herders later because during excavation bones of wild deer and pigs were found which suggest that they were hunters. Further excavation led to discovery of skeletons of domestic animals like Goats and Sheep which suggests that started herding animals.

NOTE: Mehrgarh is located in present day Pakistan, it was one of the most important routes to Iran.