You use to hear it all the time about people in Taiwan and Hong Kong, and Singapore too. Back in the day (for Singapore that's as close as the 70s), they were seedy ports, with anything goes rules, prostitution, gambling, counterfeiting, drugs, and so on. Look for old books on those places.
Those things gradually changed as those 3 places became richer and more important for trade (and Taiwan was an early "China", getting outsourced industrial production from the West).
Note that all three places are much smaller than China, don't have 600+ strong rural population still struggling to get by/to middle class by any means, and some of them had a "Delaware/Switzerland" role in the region, with multiple interests vested in that working well (which is how the law sausage gets made to benefit corporations, the rule of law is held, and the countries get "high marks" for "economic freedom": https://en.wikipedia.org/wiki/List_of_countries_by_economic_... ).
Because cheating is a cultural rather than ethnical thing.
There are ethnical Chinese people in those regions you listed, but sure mainland China sailed a totally different cultural course over the last 70 years.
In mainland china, cheating mostly happen because of over competition. If you don't cheat, others will and will crush you in business or academic competition. Cheaters go home for chicken dinner while non-cheaters goes to jail.
Also I've met a lot of mainland Chinese people who recently immigrated to the us and can say that they don't seem like unscrupulous people at a significantly greater rate than the general population.
My grandfather used to say that he left the Soviet Union because he didn't want to live in a country where you have to cheat in order to have a good life.
Taiwan was "civilized" by 50 years of Japanese occupation that wasn't brutal or repressive as Korea. Though I think Taiwan was more of a backwater island nation when the Japanese came. Likewise for Hong Kong with Britain. Taiwan and Hong Kong sort of organically grew into and internalized the modern legal and business structures laid down by the occupiers. China is having to do what Lee Kuan Yew did, which was transform an unruly, anarchic, but otherwise sophisticated culture into one that obeys and values modern legal, rules-based norms.
Also, China is a huge country with many cultures. Closer to Beijing the culture was historically more legalist and authoritarian. The southern coastal trading cultures were more anarchic. And I think that's still very much the same today, except because of industrialization and nationalization there's conflict where historically there was a natural symbiosis and passivity regarding the respective roles.
Maybe the question should be, why do you hear a lot more about it. Because China is 100 times the population of those other places? And, well, there seems a trend at least on HN lately, in stories from US papers/journals, and in the US media generally I assume (don't know, I'm not there) to favour 'China bad' stories, over 'China good' or '(Other country) bad'. It's pretty tedious, and seems to have started not long ago. It has that nauseating feeling of that regular US media obsession on the next country they'll invade/bomb. Demonization, subhumanization, whatever you want to call it.
Why though ?
Apart from looking similar they are quite different culturally from mainland China. A lot of which stems from the fact that they were former British colonies and have always taken inspiration from the West.
Now, Taiwan and Hongkong are China. But China that continued on more traditional values. The communist regime has worked hard to change the fabric of society (like it did in e.g. Russia) and that has had negative consequences on culture and manners, and brought distrust in most institutions.
It is also down to the legal and regulatory environment. Just look for stories from Europe and the Us in the 19th century and you'll find many, many stories like you could hear from China today. And those stories from China today are what happens in many countries around the world outside of the Western 'bubble'.