Why Pandavas r not called Kauravs?

many of us had the same question that why pandavas are not referred as kauravas despite of being from the same family- the 'Kuru vansh'. their father pandu was also a kuru prince just like dhritrashtra then why the family name kaurav is used only to refer to dhrit's sons and not pandu's??.

The children of Dhritarashtra[edit]

The children of Dhritarashtra by Gandhari are also referred by a more specific and frequently encountered term - Dhrtarra, a derivative of Dhtarra (Dhritarashtra).

According to the epic, Gandhari wanted a hundred sons, and Vyasa granted her a boon that she would have these. Another version says that she was unable to have any children for a long time and she eventually became pregnant, but did not deliver for two years, after which she gave birth to a lump of flesh. Vyasa cut this lump into a hundred and one pieces, and these eventually developed into a hundred boys and one girl.

The birth of these children is relevant to the dispute over succession of the kingdom's throne. It attributes the late birth of Duryodhana, the eldest son of Dhritarashtra, despite his father's early marriage and legitimizes the case for his cousin Yudhisthira to claim the throne, since he could claim to be the eldest of his generation. All the sons of Dhritarashtra excluding Yuyutsu (born of Dhritarashtra's marriage with a Vaysya woman, thus a step brother of Duryodhana) were killed in the great battle at Kurukshetra.

Quote from Mahabharata, Sambava Parva, Section CXV:^[1]

"And during the time when Gandhari was in a state of advanced pregnancy, there was a maid servant of the Vaisy class who used to attend on Dhritarashtra. During that year, O king, was begotten upon her by the illustrious Dhritarashtra a son endued with great intelligence who was afterwards named Yuvutsu. And because he was begotten by a Kshatriya upon a Vaisy woman, he was subject to the constant taunts of the Kaurava.

Thus were born unto the wise Dhritarashtra, a hundred sons who were all heroes and mighty chariot-fighters, and a daughter over and above the hundred, and another son Yuyutsu of great energy and prowess begotten upon a Vaisya woman."