The reason for this isn't surveillance or the harshness of punishments.
The reason for it was that when there's an easy default roadmap for your life (School -> Gainful employment), you're not going to drop out of civilized society, and into criminality at the age of 15.
It's not that there's more to gain from criminality now, compared to fifty years ago. It's that there's less to lose. Instead of a social contract that guarantees[2] employment, a shitty apartment, and food on your table, if you just go through the motions, it's a dog-eat-dog-every-man-for-himself world. Unsurprisingly, many people find it easier to drop out of that, and make a living through crime.
[1] Without even mentioning the truly mind-blowing amount of low-level, and high-level corruption that the USSR experienced.
[2] Employment wasn't guaranteed - people had to go apply for jobs, have their employment and social records get checked, there was competition for getting into good jobs, etc - but 100% employment was an official goal of the state. This is not the case in either the West, or the East, anymore.
During the chernobyl disaster the USSR kept providing false numbers to the world in order to downplay the significance of the event - to the point of sabotaging the cleanup effort and themselves.
Both China and Soviet Union (probably others too but I don’t know), pre-liberalization were your typical socialist state with lots of means to control people, so they did but... but people didn’t engage in much petty crime or gang crime.
Those types of crimes were more or less very unusual. But in those same states today with more tools to control people, petty crime and gang-related crime (as well as corruption but that kind of always existed), are through the roof.
And it’s not like either are soft on crime.
So what has given a rise to that criminal activity which for practical purposes didn’t exist before. Is it opportunity? That is there was nothing to gain from it before?