You must realize that not all soviet citizens opposed the USSR. Many elderly citizens of the former soviet states still talk about how they wish the Soviet Union never fell. There was security that came along with knowing that as long as you toed the line you wouldn't starve(not always true). Another large part was fear. Under Stalin any discussion of displeasure with the Soviet regime could get one shipped off to a gulag. It's tough to get any sort of movement going when you were jailed for even talking about the idea. After Stalin fear was still common. Even if being shipped off to gulags wasn't as widespread the fear still existed. The Soviet Union was also a superpower that many people felt great pride in. They held a lot of power on the worldwide level. Many different aspects led to a lack of uprising. Your question is posed as asking which reason did the USSR not have an uprising, but I would say it is all of those reasons and more.

The Bolsheviks tolerated no political deviations, even ones that from an outside perspective look like incredibly minor ideological squabbles (e.g. Bolsheviks vs. Mensheviks — two Communist groups with the thinnest of ideological distinctions). But I think even this masks the great transformation that took place in Russian society between 1917 and the late 1920s, when the Bolshevik regime was really cemented.

Russia of 1917 had many different political factions. Some were outlawed, many were tolerated. The punishments of the Tsar were, by later standards, "old fashioned." Political prisoners were somewhat glamorized in Tsarist society, their treatment was, on the whole, not exceptionally inhumane. Prisoners of the Stalin era would look back on the memoirs of those who had been imprisoned under the late Tsars with wonder — you could have a successful hunger strike under the Tsar, and actually get reforms accomplished! (The Stalinists would, unsurprisingly, let you starve.)

Enter the revolution, which was not a Bolshevik revolution, originally. It featured the Tsar abdicating — not getting "overthrown" so much as "cutting his losses." It featured a democratic body, the Duma, taking over the country, it featured a provisional government. It was a pretty liberal, inclusive revolution as far as these things go. This is the February revolution of 1917.

Later the Bolsheviks took over, in the October revolution. Now this was a Communist revolution, and in the name of ideology tolerated little political dissidence. Non-Bolsheviks were barred from political power (but not yet truly "purged"). This led to the bloody, protracted Russian Civil War (1918-1923), which like most civil wars radically disrupted the country, made loyalty a paramount issue, and took the already-pretty-not-nice Bolsheviks and made them into a party that saw mass imprisonment, mass execution, and a mass police state as a good solution to their overall ideological problem, which was that they wanted a very different society than existed (and, arguably, had ever existed), and their practical problem, which was that they wanted to stay in power with no challengers.

At the end of the Civil War period, Lenin dies, Stalin takes power, and whatever an unpleasant guy Lenin was (and he was one), Stalin was a millionfold worse. Stalin re-arranged the social, political, and economic situation of the country in massive, often haphazard and terrible ways. Under him the secret police situation grew enormously, and the (already pre-existing) prison system expanded into a massive labor camp empire. Purges, show trials, total control of media and public life — as well as the totalitarian propaganda, cult of personality, and hardship — effectively destroyed any last remnants of Tsarist "civil society" that might have encouraged people to hold contrary points of view, much less try to wage active revolution.

The key thing here is not to see the Tsars as great (they were not) or the Bolsheviks as evil (they were not). It is to see that Tsarist rule was weak and on the wane when the revolution happened, and had already been liberalized, diversified, and reformed to a degree that the idea of organizing an overthrow was feasible. (And World War I did not help.) The revolution did not end that immediately, but as the Bolsheviks consolidated power, and touched off a civil war, it created the opportunities and pretexts of actually sweeping away all of those reforms, and making things much more repressive than had existed in the final years of the Tsar. A better comparison would be to compare the height of Tsarist power and repression with the Bolshevik takeover, and the end of the Soviet Union (i.e. Gorbachev's reforms) with the end of the Tsars.

Coups and revolutions are tricky and political (obviously). Even the simplest coup will inevitably involve dozens of demographics, including religious / ethnic groups, political parties, and economic classes, each with a different experience of the ruling powers. The Russian revolution occurred during a time of economic and social change. Russia, like much of Europe, experienced rapid urbanization and industrialization and WWI wasn't going very well for Russia at the time, resulting in massive casualties, food shortages, and inflation. When the protests that eventually became the revolution cropped up, Russia had very few troops on the home front and many of their troops were new and untested or wounded in battle and they were quickly overpowered.

All that to say, revolutions are unpredictable and they crop up out of a variety of interrelated conditions, including opportunity and chance, not just out of the brutality of conditions. Throughout history people have faced brutal and repressive conditions, but the ability to respond to those conditions and the way people choose to resist or respond is massively complex. Simply because a country has previously been successful in overthrowing a government in no way predicts their success overthrowing a different government in the same way that winning a war doesn't predict success in the next war.

It's not that easy to say that the tsar was overthrown. At the end of the war, the executive powers of the Russian Empire basically dissolved. The following war isn't a revolutionary war between uprising people and the government it is a civil war over the question where the new state is heading politically.

Also your question is all over the place. The Soviet Union covers 70 years, and while Stalin is an important chapter it is not everything. While living conditions under Stalin were harsh, you have to see that the remnants of the Civil War were still fresh. The Civil War was unbelievably brutal. It was cruel and the difference between military and civilan population vanished more and more. Nobody wanted war any more. Also, while living was harsh, economic advancement under Stalin was rapid. Also the Soviet Union came out of WW2 as a victorious Super Power.

After Stalin the Soviet Union became an authoritarian dictatorship, that while it had little political and personal freedom provided a better living standard than ever before in Russia. Russian GDP only surpassed the last year of the Russian SSR only a few years ago, but with a much higher wealth disparity. And political freedom is still low.

In Aleksandr Solzhenitsyn's Gulag Archepelago he alleges that the Soviet government was far more oppressive than the Tsarist regime. Agitators, many of whom became Soviet leaders, were merely exiled to distant towns and could slip away easily. Those who were caught suffered no extension in their sentence and those who helped them on the way were in no danger of running afoul of the authorities. In the Soviet era escape meant another ten years on one's sentence or death and the incarceration in GULAG of anyone that helped them on the way.

He also describes that in the tsarist era prisoners were routinely given amnesty and that the public would frequently give them food and supplies. Then the political prisoner was held in high regard and was essentially the equal of his jailer. In the Soviet era this was reversed: the political prisoners got the harshest sentences and amnesty was unthinkable. The public wouldn't dare support them because such support could land them in prison as well.

Additionally, all that was required for someone to have a conviction for political agitation (Article 58) was for someone to inform on them, and such allegations were frequently made under duress. This led to a general suspicion in the public as children could turn in their parents and spouses could inform on each other. All of these factors pretty much destroyed the possibility of the nucleus of a rebellion from forming.

Getting a political sentence was tantamount to the death penalty in most cases. Those accused and convicted by a rubber stamp troika would spend 10 to 25 years performing hard labor from dawn to dusk on bread rations of around 10 grams a day and sometimes given thin gruel. In addition to the work, the cold sapped calories and everyone was essentially starved to death while doing make-work. Add to this the fact that the working areas and jobs involved were very unsafe and a political stint usually meant death.

The difference between the position of the populace in tsarist times and the post revolution times is quite huge. Many people were unfree serfs in Russia prior to the revolution and after that they had (or were supposed to have) a stake in society. I would speculate that early on many people would be quite empathetic to the new regime but then it gradually got worse until they found themselfs in a new absolutist/totalitarian state.