A system is just a thing that happens when people act. Corruption ballooned in the USSR because it was based on multiple levels of patronage from the start. People with any real intellectual capacity were used up, executed, driven mad, or excluded from ‘the system’ - the networks of patronage - early on. No petty ‘boss’ who thinks his word is law wants someone smarter than they are around. From the bottom to the top all relationships were based on favours, the parroting and acceptance of lies that could change from one day to the next, and the need to keep whoever was above you happy. Corruption is a normal part of those kind of arrangements. Some people, like Putin, of limited intellectual capacity, actually bought into it all, really believed it was good and the collective West was some hellhole of exploitation and drug addiction.
People accept what happens around them as normal. There is a lot of writing about this sort of thing, but not in all history books. It depends what you are reading.
The same thing persists in Russia - a couple of years ago, North Korean was the butt of all kinds of ridicule on the ‘patriotic’ TV shows. China was viewed with suspicion. Now NK is a glorious defender of truth and justice, an advanced, modern society (‘look how wide the roads are’ is an actual quote from some dumbass propaganda show. People are fully expected to nod and show appreciation (people do this even in their own homes), and China is everyone’s friend. This sort of thing is so normal in Russia it barely registers. Imagine if everyone you know started talking about how great and honest Trump is tomorrow, and when you questioned it they just gave you blank looks and carried on as if you just didn’t ‘get’ it. If you actually think in that kind of society you soon find yourself on the fringes of it, if not actively being persecuted by the ‘believers’. Look how fast Russia went from relatively normal to a guy being locked up because his daughter drew a picture of Russian aircraft bombing civilians, and school and university students shopping anyone among them who criticises the war.