Yeah well, you see... After dating a girl from China and getting connected to more Mainland Chinese people (my heritage is from Taiwan), Traditional culture in China was all about karma and being almost over-the-top cordial (at least in a Westerner's perspective) to each other. However, ever since they have opened up trade and cheap labor, it has become a very dog-eat-dog culture driven by greed... They have evolved into becoming a very ruthless and corrupt culture, so distrust is rampant, and just about anything done or said in China is met with lots of skepticism. People are hesitant to eat out since their foods are cooked in
gutter oil and there have been numerous interviews where CEOs of food companies don't even dare to eat their own products, supplements are often just placebo fillers, and just about anybody who has some connection with the government can bribe their way out of just about anything...
Aside from those that are doing it for the purpose of commerce, among the main reasons that people are leaving China in droves is because of the fucked up culture.
With that, also with the "one child per household" law and no abortion laws, most families strived towards having a son, so women are somewhat scarce and prone to fierce competition, which results in even the most worthless of women (like ones who don't cook, clean or suck [both literally and metaphorically], my ex included) being put on a pedestal, with the man doing everything for them and let them go crazy shopping... Meaning it's perfectly acceptable for her to sit around and watch TV all day while the man does everything, while it's grounds for separation in American culture since it's unfair... It's even gone as far as retaining an ancient tradition of a
bride price, often anywhere from $2,000 USD and up (my ex's family wanted $20,000, which was among many reasons I left her ass and vowed to never date anybody from Mainland China again) to make themselves ever so much the "asset" of the family.
Also by extension of greed-driven culture? If a bystander gets involved, they can press charges and/or sue the bystander to be guilty by association, accusing them of being involved somehow, like helping a fallen old man up results in being accusing of pushing him or causing him to fall, which has
made headlines multiple times, so people lay in the streets for long times with nobody daring to help them out. In fact, there's even a popular
joke about about Santa falling and Christmas being canceled since nobody dared to help him up.
With all that considered (TL/DR), another hidden motive may be that the fight was driven by greed and distrust, which they don't want the woman to have their money/reverse dowry, and the bystanders didn't want to help since they may be considered an accomplice.