As for why she left? Well, it was simple enough. Old Wang had only been in the Southern Continent to gather some ingredients. It wasn't a long term thing. And seeing as she had no real reason to stay in the Southern Continent, she left.
In any case, after killing and slaughtering for so many years, the amount of funds she had left over was no small amount. After all, Bai Ming made a living by killing the equivalent of Nascent Soul Stage and Resonance Stage cultivators. The amount she was paid and was able to loot from just one bounty was an amount most wouldn't see in their entire lifetimes.
