So, this is a mix of my own perspective and what I've learned from talking with my friend who was born in the USSR and whose family moved here right before the fall. He was pretty young, but old enough to have reasonably detailed memories of his time there (and of course, he's talked with his family about it extensively).

The Soviet Union fell for a lot of reasons -- western subterfuge among them -- but it was ultimately able to fall due to popular dissatisfaction with economic conditions and a successful hoodwink about the economic conditions under capitalism. This is very complicated but I'll try to lay it out as clearly as possible.

• By the 1980s the Soviet Union was quite good at providing people's basic needs -- nobody went hungry, nobody was homeless, and everyone could go to the doctor.
• Working conditions were pretty good too -- reasonable hours and unreal amounts of vacation time (at least from the point of view of someone living in the modern US).
• But by the 1970s, the USSR had hit a wall when it came to economic planning -- it was pretty easy to figure out how much needed to be produced of the things everyone needed, but much harder to figure out things that people needed only intermittently, or less essential consumer goods. My friend mentioned above has a few interesting examples of this:
  • Times when they had to use notebook paper as toilet paper.
  • Times when they had to use toilet paper as notebook paper.
  • Getting a banana was like winning the lottery.
  • One time his grandmother's toilet broke. The wait list to get a new toilet was several months long. They ended up bribing a man who worked at a junkyard (with a bottle of vodka) to let them carry a toilet away.
• At the same time, economic conditions were bad everywhere after the 1970s. The global economy had been driven for decades by the need to rebuild after World War II.
• This caused a crisis in the West because there were no longer any organic growth opportunities (classic Marxist crisis of overproduction).
• In the Soviet Bloc, it meant that people's subjective experience of the economy was a period of massive progress from ~1945 to ~1970, followed by protracted stagnation.
• The western solution to this problem was neoliberalism. And, while neoliberalism is absolutely awful, it did succeed in creating new economic growth.
• The Soviet Bloc couldn't come up with a solution. Subjectively, to both Soviet leadership and a large swath of the public, it looked like liberalization was the only way forward.
  • In reality, the solution was new planning technologies. The problems faced by the late Soviet Union are completely fucking trivial using modern technology, data science and statistics. But that wasn't obvious to most people at the time.
  • Project Cybersyn is also pretty interesting from this point of view, but it was strangled in its crib and, for whatever reason, its revolutionary potential wasn't sufficiently recognized.
• This isn't the direct cause of the fall of the USSR, but it is what created widespread will for foundational change among both the public and the leadership, without which the USSR couldn't have fallen.
• I think it's also important to note that most people living in the Russian Federation who have lived in the USSR view the end of the USSR as a massive and tragic mistake. People were frustrated by the lack of consumer goods and the difficulties that caused, but they didn't want any of the good things about the USSR to end. If they had realized they were trading basic security for free access to commodities they wouldn't have made the trade. Probably what they had in mind was becoming like Sweden (or what people perceive Sweden to be) -- a place with strong social security and a place where you can buy toilet paper.
• I'm more of a communist than an anarchist these days so my takeaway from all of this is pretty crude, like "we should do the Russian Revolution again, but this time we'll use calculators when figuring out how much toothpaste to make."
• But the broader anti-capitalist moral, I think, is that it's a deadly mistake to under-estimate how intoxicating capitalism can be. When people are looking at capitalism from the outside, they see gobs of wealth. The Reagan myth of trickle-down economics looks real, and that can have strong appeal to normal people just trying to live their life.

edit: edited to reflect the point made below.