Thinking about MDZS politics again and how precarious everyone's positions post-war are so fascinating.
1. The Wens ransack the Cloud Recesses and this is particularly devastating for that sect because they are not an economic centre of their own, but rely on drawing in nighthunting jobs and students to 'pay the bills'. Without their centuries of collected knowledge and natural cultivation-enhancing spaces, they don't have a practical method of day-to-day sect survival available. Caiyi town, their lifeline (waterways are EVERYTHING in economics it does not matter that they can fly) is crippled before the story even starts. While the Lans aren't outright killed as the Jiang are, the Wens clearly intended to starve them out.
2. This strategy WOULD NOT work in Yunmeng, which is not geographically or economically isolated, and in which the cultivation clan is shown to participate in agriculture and acts as a trade interface. Because of its position, it also makes an excellent hub for the further control of surrounding regions (again, WATERWAYS.) So of course it has to be physically 'taken over', necessitating the extermination of the entire clan + anyone else unlucky enough to have been at Lotus Pier that day. With YMJ under their control, none of the minor sects can do much, so they're 'left alone' (have their weapons stolen but not exterminated). The Wens now control the region's trade. Even cultivators need to eat, to repair clothing and armor, to get access to medicine. This is also why Wen Qing running a supervisory office *is not morally neutral* even if she isn't actively fighting non-Wens. Her presence and oversight are part of ensuring an economic chokehold on a region that directly supplies and bolsters the Wens efforts elsewhere.
3. The fact that the Jiang sect was even 'allowed' to rebuild after the war instead of being forcefully taken over/administrated by another clan (the Jin, it would have been the Jin. They had marriage ties to justify it socially and legally, and the manpower from their late entry into the war to enforce it) reads to me as a combination of a couple interesting factors:
3.1 The fear of Wei Wuxian/demonic cultivation - which further contextualises WWX's exit as him not just abandoning JC as an individual but jeopardizing his clan as well. Which I think is obvious but people do forget at times.
3.2 The degree to which the Jin are committed to their benevolent self-image and how much political sway that lends them.
3.3 The continued capitulation and overtures from the Jiang sect towards their nearby allies and the great sects who stand to benefit from having such an economically-rich region well-managed without having to sacrifice their own manpower, but still be something they greatly benefit from. This is JYL's marriage, the grace of having one of YZY's greatest friends as the mother-in-law; unfavourable trade deals, giving up salvaged artifacts and stretching their people thin attempting to both regain wealth and trust from citizenry through nighthunting.
3.4 Nie Mingjue (and SL Yao) - really the only sect leaders who consider honor foremost in their political decisions, and therefore the most likely to support the continuation of YMJ ideologically, as the rightful recapturing of stolen land/act of rightful revenge. This remains contingent on YMJ's continued adherence *to that regime of revenge*.
4. The rebuilding of Cloud Recesses is similarly rife with complicated politics, chief of which is Lan Xichen's need to please Jin Guangyao, through which the Jin offer financial aid to help physically rebuild infrastructure. (Not that they aren't genuine friends, but their political relationship is very much part of things). Recall also that, in order to draw in students, Gusu Lan has to present themselves as righteous as per the societal definition of righteousness, internal moral reasoning aside.
5. The Wens' destructive/disruptive path through cultivator society was so widespread and thorough and well-planned, that it's little wonder literally no one has any goodwill towards people surnamed Wen in the post-war. Consider this: there were servants/merchants/visiting families/fishermen/ordinary folk who were killed or had their livelihoods ruined by the Wens during their regional takeovers. Does the blood of only the cultivator Wens make up for these lives too? Were they not themselves innocents who just so happened to be around Yunmeng/Caiyi Town/the Cloud Recesses/delivering food to the Clan hubs/weaving cloth to sell to the cultivators/picking their herbs/excitedly showing their children the cultivators flying by? Just think about this, and come to your own conclusions, on the difficulty of assigning blame and innocence.
6. What the cultivation world did in turning around and killing the Wen remnants was inevitable. The participation in that extermination of characters we otherwise like/support was also inevitable within the confines of the political and social structures they inhabit. Just as Wen Qing's supervisory role was, and Wen Ning's leadership of his Wen squad was. This is part of the tragedy of all of it. MDZS is not a story about wandering cultivators in the Jianghu who are neither beholden to the rule of politics nor have any collateral supports endangered by their action/inaction. Xiao Xingchen and Song Lan come at the problem with the hope that it is nepotism that corrupts this system, but This Is How Political Systems Function. So long as the cultivation sects exist as sects with complex economic ties to one another and regular regional+ economics, all of which are entrenched in a society with particular values (all of which reiterate the preservation of the sect/clan and these structures and relationships) this will be the reaction to these kinds of events.
