It may have been the case where China had NOT actually wanted to choose this period of time in history to re-ignite this border or chose to respond this way to the moves by India since Doklam crisis. But rather it was really India that built up that momentum since budging in to the Bhutan China dialogue in 2013.
Perhaps India chose to inflame at this point in time not just with Doklam and increased salami slicing but also art. 370, road building, and threatening CPEC along with greater degree and depth of patrols to which PLA eventually was ordered to respond with activities since May 2020. I'm not blaming Indians. They legitimately see it as their land and then some and they do have better reasons in all honesty. Not from historic borders but from the simple fact that these parts are much closer and threatening to them since they are within even long range artillery fire of a lot of their dense northern urban areas. Anyway.
It would make sense if all CCP wanted from PLA's move and settlement more than half way into the disputed western section between valley and lake, was just to get absolute written agreements from Indian government that there will be at least no more IA patrols up to finger 8 and associated Indian recognised borders and no more road building/ construction nearby. If those conditions are met along with total withdrawal from IA back to behind finger 3, the PLA will move behind finger 8. This would really mean China was never ahead to begin with and India delayed agreeing to conditions even after PLA captured all that land because India was ahead to begin with and wanted to keep trying different wants to maintain their lead.
The reason for India eventually agreeing to something they never really "owned" is totally an internal matter and partly if not mostly due to internal instability and the crisis building. Along with of course PLA's pretty daring move to take more than half the dispute in one swooping response. What made the CCP pull back PLA with disengagement was India's agreement to China's initial theoretical conditions of no more activity and inflaming and the old "wait for future generations". Just another theory though.
This theory just shifts the understanding of the picture formed a little more to India's side from the very beginning. China can do nothing about India's threatening of CPEC and Kashmiri self determination it seems.
