Simply because Beijing till this day does not possess any historical documentation required for proving its territorial claims based on traditional and customary practices of the past, as disclosed below.
China Began Violating The 1954 Panchsheel Treaty From 1955
Tibetan Ficklemindedness & Its Govt-in-Exile’s Ambivalence On The Status Of Tawang
India’s Unstated Territorial Claims Inside TAR
(To Be Concluded)