The Hundred Billion Dollars Question: why Tibet was liberated?

On December 1949, the Government of India foolishly decided to hurry the recognition of the new Communist regime in Beijing.
The next morning the New China News Agency (Xinhua) proclaimed: "the tasks for the People's Liberation Army for 1950 are to liberate Taiwan, Hainan and Tibet... Tibet is an integral part of China. Tibet has fallen under the influence of the imperialist."
During the following months, China never missed a chance to assert again and again that Tibet was part of China's territory and it was "China's sacred duty to liberate Tibet."
But what was this ‘liberation’ about? Why was it a 'sacred duty' for Communist China?
The Tibetans could not really understand why they needed to be ‘liberated’.
Over the years, the Dalai Lama and his countrymen understood that the Communist leadership in Beijing needed their country to control the rivers of Tibet, to occupy a strategic position vis-a-vis India and to spread their brand of Communism over the high plateau (and then Asia). It took more time to realize that China was also after Tibet’s minerals.
The railway line to Lhasa ‘liberated’ further Tibet, now the Chinese can take away the underground wealth. A hundred billion dollars business.

China to develop three major mineral bases in Tibet
Agencies 
February 07 2011
Beijing: China plans to develop three major mineral bases in Tibet in the coming five years amid reports that 102 types of deposits with an estimated value of USD 100 billion have been discovered in the region.
The Tibet Autonomous Region will step up the exploration of copper, lead, zinc, chromium and gold in its central areas, including the regional capital city of Lhasa and Shannan Prefecture, to form a major mineral base for non-ferrous metals and chromes, the state-run Xinhua news agency reported.
A non-ferrous metal base will be established in Qamdo Prefecture in the east of Tibet, an area with 15 million tonnes of proven copper, lead and zinc reserves in the new five year plan starting from this year.
In addition, a salt lake area in the northwest of Tibet is expected to become a major base for saline minerals and lithium, the report said.
Last December, Chinese official media reported that geologists discovered 102 types of mineral deposits in over 3000 mine beds with an estimated value of about 600 billion Yuan, (USD 100 billion).
Among the variety of mineral reserves, Tibet is reported to have large chromium and cuprum far higher than other regions of mainland China. Twelve other mineral reserves rank among the top five across the whole country.
Chinese aluminium and copper giant Aluminum Corp of China, or Chinalco has already set up its unit there, besides Chinese miners Western Mining Co and Zijin Mining Group Co Ltd which already started production at the Yulong copper deposit, in southeastern Tibet.
Access to the remote Tibetan areas is no longer a problem as China has already built enormous amount of rail, road and air infrastructure connecting TAR with the mainland.
The rapid exploration of natural resources and development of infrastructure evoked criticism from the Tibetan say this would benefit the main land more as it fuels influx from the outside the region besides harming the plateau's fragile environment.