Here's why it happened, from a strategic perspective.
There is only 1 road connecting India and China - a very mountainous road going through Tibet which is easily defended or destroyed by either side - just bomb a cliff once every couple of weeks and block the road.
The other borders with China already have plentiful PLA equipment and personnel in place, there are no connected roads and the terrain is unfavorable.
Burma has multiple routes directly into the heartland of China which aren't easily destroyed (wide roads on flat terrain and not too many bridges/deep rivers).
Going through Burma is the only realistic strategy for some of the 1.4 million active Indian military to invade mainland China (perhaps a joint invasion with the US and others).
If Xi is white hat all along then the CCP is as good as dead already - if not then taking Beijing is 90% of the job.