It happened more than 70 years ago. What would be the point? I remember my mum wearing a Free Tibet t-shirt in the 90s, but even then it was a fait accompli.

Because it hasn’t resulted in a stable situation or a historical event that stops being relevant to the current moment. No harmony has formed since. It is still essentially an ongoing invasion and erasure and oppression of Tibetan culture and people. See moves related to giant damn building most recently, but it is has been continuous, and there are big concerns among Tibetans about it getting worse still in the future, when the Dalai Lama dies. Only the initial maneuvers of invading are in the past, the rest applies to the current moment, day by day.