I'm not a ricecel but from research I've done I can say this: all of East Asia is suffering from the same problems as western countries that comes with urbanization. That is, women are less directly reliant on men so they become pickier and choose to focus on their career over starting a family. This effect becomes even more pronounced the faster a country urbanizes, and in China and Korea it has happened in the span of 2 or 3 decades which is fucking insane.
However in East Asian societies there's still enforcement of gender roles to a large degree, so women who do get married and have children are expected to remain a housewife rather than continuing to work while raising children. Therefore even more women avoid starting families than in countries where such expectations no longer exist. Though I'm not sure if that's as true for China because communism erased so much of their old culture and values. However the sex inbalance is so great that a huge number of Chinese men are guaranteed to be incel, no getting around that.
Declining population contributes as well. Since older men naturally will lay claim to younger women, especially in East Asia where seniority grants much greater status, younger guys have access to a dwindling pool of women. This is most pronounced in Japan due its demographics but Korea and China are right behind them.
The only upside is that women over there at least try to appear feminine and gender roles are enforced to a much greater degree. And there's little to no promotion of LGBT or racemixing like in the West. For China one good thing is that much of the country is still rural, so maybe there's a chance to get with a country girl. In Japan and Korea I think only old people live in the countryside anymore so there's not even that.