All you said in regards to male/female ratio is true, and single women have lots potential mates to choose from.
Unfortunately, the mistress situation is still common, due to a variety of issues around limited supply of wealthy men, divorce laws favouring the wealthy, societal stigma against divorced people, social norm of judging men by success and women by look, etc, etc.
Not all those issues are female-centric, but combined, they make it acceptable (while still looked down upon, if advertised) for some women to be a mistress of some powerful man, and powerful men to have mistresses.
This is because of the "stake" people are seeking when looking for a marriage between genders. Women are seeking wealth, social status, personality and whatever it may take to maintain a stable marriage ( family). While men, in most cases, are looking for prettiness, good-looking or whatever superficial. This kind of value lifespan and marriage purpose mismatch is the whole problem of marriage issues in China.
A divorced, less pretty (compare to those in 20s), mid-aged woman is very hard to find another marriage. Even if they did not even marry before, it is still hard for them. A lot of women in China who are well-educated, well-paid, in their 30s still have problems in finding partners (This is what Chinese society called sheng nu, or "women that left behind":https://en.wikipedia.org/wiki/Sheng_nu).
Statistically speaking, women are indeed more than men, but the mating process is not statistic.
Now it would be fascinating if people could generate probability distributions that accurately describe social-economic systems/relationships like what I would say that you accurately describe quantitatively.
Besides, it's not like this is for the general population. Mistresses are a common trait in the upper classes -- which, in a huge place like China, are still in the tens of millions...
The ratio of females to males that women actually want is balanced the other way. And it's that way pretty much everywhere in the world.
A f/m << 1 just means there are more men to settle for, not really to choose.
By the way what is that movie's actual name? I haven't been able to find it on imdb, rotten tomatoes, etc.
Granted, this often breaks down such as with the last mortgage crash but no abstraction is actually true.
And when you buy beef in bulk, that doesn't mean that they'll send you whatever meat they have on hand, nor is that what 'fungible' even means.
Electronic money, Stock etc are defined as Fungible because two people can exchange tokens of ownership in the same thing without impacting anything. The same is 'said' about crude oil and other physical thing even though they are not actually identical they are treated as such.
However, the same effect happens when company's own huge set's of IP. That IP is treated as an income stream and money does not care about it's origin. The reverse even happens with money. Coins as collectors items are independent from there nominal value.
For a back and forth example. Two Kids might trade 1's because the Serial Numbers of one of the bills contain 666 which lowers the value to one and increases it to another. Later if the bill is spent it could go though a hundred transactions where nobody cares about the SN.
The services in the article cost upwards of $10k which means the woman in this case might be married to a rich high status man, which is arguably difficult to come by.
If you are a women age 28 married to a high status man for say six years, you probably want to keep that man instead of trying to find another one.
The woman does not get a copy of the man's status.
She gets high status by marrying a high status man.
The wife of Donald Trump does not have to achieve anything to gain status. She gains status simply by being Trump's wife.
China female/male ratio is heavily unbalanced. There is a LOT men on market for women to choose. Also almost no foreign woman marry chinese man, on the contrary to the chinese women marrying a lot of foreigners.
1+2 means china is a market where men are at bad position and women has plenty of fish to choose from. Opposite situation which would create such services as described in the article.
Source: https://en.wikipedia.org/wiki/Missing_women_of_China
According to 2012 figures from the National Bureau of Statistics, China’s sex ratio at birth (the number of boys born for every 100 girls) was as high as 118.