China wants to trade with everyone, we are the largest trading partner of most countries in the world (including Japan).
While India wants to trade based on emotionalism. India-Pakistan trade is already abysmally low despite sharing one of the longest borders in the world, even before they wanted to seal the border.
And sealed borders mean that both sides have less invested in the other, therefore greater likelihood of war (even nuclear war).
This is the same reason India is refusing to participate in China's One Belt One Road initiative. I don't understand why India has a problem with increasing economic cooperation in the region, preferring instead to hold business ties hostage to emotionalism.