the term "pig butchering" originates in Chinese (杀猪盘), where this particular style of scam is often targeted at overseas people via WhatsApp. So "pig butchering" refers specifically to these scams run from China (or elsewhere in the region by Chinese operations), and it's what the scammers themselves call it. One of the distinguishing features is that they're often run by fairly large, organized operations with paid, trafficked, or otherwise long-term staff manning the WhatsApp personas. Similar to Indian call center scams.
Much like how "419" or "Nigerian prince" refers to scams coming out of a specific region.
I still don't get it. Is pig butchering a common phrase in Chinese to refer to scams? I believe the phrase, even in its original Chinese language, was only invented recently (Wikipedia says 2016). That doesn't answer the question of why this particular phrase was invented.
That being said it's not just Chinese people targeting overseas people. Chinese people are also often targets of pig butchering. The problem is so bad that a movie was made about it in China and earned $500M at the box office. Given that China heavily censors its media market, it is no secret who is doing what. https://en.wikipedia.org/wiki/No_More_Bets
I always thought it was because they are looking for big victims loosing a lot (fattning up the pig and then butchering it) vs scams stealing small amounts from a lot of people.
Much like how "419" or "Nigerian prince" refers to scams coming out of a specific region.