Why are people investing in emerging markets, a more risky asset class when the market is highly volatile due to uncertainty between the trade war?

Short answer to your question is that High Risk, High Return.

Indeed such economies may be volatile as you have rightfully pointed out. However, it can be seen as an opporunity since emerging markets are likely the next growth spurt. It really depends on your investent horizon when it comes to this type of investments, if you are able to hold it up through the storms, likely that you would benefit from the opportunity.