When one can find no reason for studying, getting a job, marrying, having children, or life itself, refusal to do anything is a natural reaction. Remember, religion is not exactly taught in China except as an evil Western, capitalist device to control the people. Ironically, since Communism is itself, a religion, Lying Flat is the end product!
I can’t say I blame the young people who are into the third and fourth generations of Communism. How many in China today were alive before the Cultural Revolution? It’s almost out of living memory.
We may not call it that, but we’re well on the way to the same thing in the West, including the USA. People in their 40s-60s have grown up without religion, without morals. Once the allure of the world and materialism wears off or is rendered unattainable, what else is there? Why not just crawl into a corner and die? Or flop on a park bench, go to sleep, and hope you don’t wake up?