Many of the Greeks, Kushanas and Shakas embraced Buddhism rather than Hinduism because

1. Many foreign groups like the Greeks (Indo-Greeks), Kushanas, and Shakas integrated into Indian society over time. 2. While Buddhism was indeed prominent (ascendant) during periods when these groups entered India, a major factor attracting them to Buddhism over Hinduism was the latter's rigid caste system. 3. The hierarchical and exclusionary nature of the caste structure in Hinduism made it difficult for foreigners to find a place, whereas Buddhism's relative egalitarianism and lack of emphasis on birth-based hierarchy offered easier assimilation and access to Indian society.