Why do literary Hindi and literary Urdu use different kinds of vocabulary?

Literary Hindi and literary Urdu utilize different vocabularies primarily due to a 19th-century process of linguistic standardization that became increasingly influenced by religious and communal identities.1

While both languages share the same Indo-Aryan grammatical and phonological base, their literary forms diverged as part of a broader effort to define distinct cultural standards. During this period of standardization, proponents of Hindi increasingly drew upon Sanskrit for formal and literary vocabulary, while proponents of Urdu drew upon Arabic and Persian.21

This divergence was further cemented by the use of different writing systems: Hindi adopted the Devanagari script, while Urdu utilized a modified form of the Perso-Arabic script known as Nastaliq. Although these literary standards remain distinct, they are mutually intelligible and share a common vernacular foundation, often referred to as Hindustani, which continues to be used in ordinary communication.21