Their low business class fares might be attractive to those who are paying their own fares but want more than being jammed in like sardines in economy.
The jump in benefit from an economy seat to a lower end business class is considerable. The jump from lower end business class to higher end such as CX and SQ is quite noticeable but may not be worth the extra couple of thousand $$ to someone not on an expense account.
The backpackers will of course choose the cheapest fares and China Southern quite often offer them on the kangaroo route.
Corporate passengers and higher end economy will probably stick with the quality airlines, particularly if wanting a stop over en route.