Tibet is home to the Himalayas, with peaks like Mount Everest. So the high terrain leaves little margin for safety in case of an emergency descent.
In the event of cabin depressurization, oxygen masks provide only a limited supply. Pilots must then descend the aircraft to a safer altitude, which is dangerous in mountainous regions like Tibet.
The rugged, mountainous terrain of Tibet offers very few flat areas suitable for emergency landings, making it a high-risk zone.
The Himalayas experience severe weather conditions, including turbulence, strong winds, and sudden storms, which can make flying dangerous and uncomfortable.
The mountainous terrain disrupts radio and radar signals, complicating navigation and communication with air traffic control.
In case of one engine failure in twin-engine aircraft, the aircraft must descend to a certain altitude, while in most of the Tibetan region, the altitude far exceeds this minimum emergency/safety altitude.
Tibet is a politically sensitive region, and some airlines avoid flying over it due to diplomatic and regulatory complexities.