China’s Tinder Suspended in Chinese Appstores: Hookup Culture in the Crosshairs? (radiichina.com)

The thing is, when the laws of a country aren't firmly grounded by rational thought and backed by relevant evidence, things become illegal simply by decree.

With that in mind, it's very possible that simply using the app to search for sexual partners is the illegal activity. The app matches individuals in way that might not happen in ways foreseeable by the economic planners, and that could prevent a harmonious society planned by government officials.

Prostitution is illegal in China and a significant proportion of the female profiles on any dating app are probably created by pimps fishing for customers. That said, enforcement against platforms for facilitation is somewhat random. E.g. the article mentions Tantan being taken down while Momo stays up.

According to this article, a video showing prostitutes receiving training on how to most effectively use Momo went viral a few years ago:

https://shanghaiist.com/2013/02/28/chinese_prostitutes_learn...

Momo is now Tantan's parent company.