Short answer: A mix of guilt, natural intelligence and supressed energy - and because there wasn't another class they could have come from.

Long answer:

Without dwelling too much in the hypothetical, start by asking yourself: what do you need to be a revolutionary?

You’d likely need time, reading and communication skills, funds, motivation, and, most importantly, an ideology.

In Russia, as in the late 1800s and early 1900s, people who fulfilled the above requirements tended to be from the bourgeoise.

Let’s rewind, back to a brief overview of Russia and its earlier versions of revolutions.

Previous Russian revolutionary movements were mostly restrained to peasant uprisings, which hit their peak in the 1700s. For the Romanov emperor in power, the thought of assassination at the hands of relative commoners was unthinkable.

Then, there was the Decembrist revolt of the 1820s, in effect an officer-led military coup which failed. Yet as a Decembrist figure would so accurately proclaim in the years afterwards: “One spark will start a flame.”

This prophecy would prove accurate – but was the best part of a century in the making.

The technological, scientific and sociological changes that happened in Europe in mid-to-late 1800s would then give rise to plenty of revolutionary thought. And plenty of this revolutionary thought would take place in Russia.

Yet aside from the historic (and by global standards) the late liberation of the serfs in the 1860s, changes in Russia were to prove gradual. All power was still in hands of the Romanov emperors.

Parochial concerns

For most people in the Russia at the time, such as the peasants, who were illiterate, isolated and bound in traditions, some kind of national or global revolution was not of any interest.

Most peasants cared about their own parochial concerns – and most of the upper-tier nobility cared about their status in society.

We’ll return to this topic of ‘who cares about a revolution’ slightly later.

And as a largely agrarian society, in the second half of the 1860s, Russia had few bourgeois to speak of.

At this time, alternative political thought in Russia was mostly confined to the few academics or people from high-enough birth to see things beyond their own local concerns.

Earlier proto-revolutionary writings usually related to the conditions at hand: such as agrarian socialism, or populism, written about by Alexander Herzen. Then there were the writings of anarchist Mikhail Bakunin, the utopian socialist Nikolay Chernyshevsky, the alternative Christian worldview of Leo Tolstoy, etc.

Herzen was the illegitimate son of a noble. Bakunin, too was from a noble family, as was Tolstoy. Of the above figures, only Chernyshevsky, a priest’s son, was far less blue-blooded. Yet as a clergyman’s son, he was of course literate.

Does guilt and shame about being from a higher class fill their writings? No. Yet one can say that these earlier writers definitely felt deeply about the situation in Russia at that time, and were keen - at least in their minds - for change.

In the late 1800s, young Lenin (himself a minor nobleman’s son) and his contemporaries - who would later form the Bolsheviks in 1903 – became interested in a new ideology, drawn from the writings of Karl Marx. In Marx's thinking, history is a series of class struggles - or a continual conflict between the oppressors and oppressed, both who hold opposing interests.

What was forming from Lenin and his colleagues was a revolutionary ideology that, for revolutionary purposes, worked where it needed to work: in the centre of fledgling Russian industry that was St Petersburg - one of Russia's few islands of progress in an ocean of agriarian backwardness.

Crowded market

Yet while we see tend to see Bolsheviks as existing in some kind of vacuum- with their party on one end, and the Russian state on the other - the Bolsheviks were just one of many groups that sprang up in the last decades of Tsarism. There were also their fellow Marxists rivals, the Mensheviks, the Socialist Revolutionaries, the bourgeois-led party for the peasants, Jewish labour groups known as bunds, the Constitutional Democrats, known as the Kadets, to name just the big players.

Overwhelmingly, these parties were staggeringly unrepresentative of the Russian population, and alien to the average Russian person.

The above-mentioned peasants, who made up 8 in 10 Russians, cared mostly about better-quality land to grow their crops - and more of it.

Meanwhile, Russian workers – who were often little more than peasants who’d moved to cities – had trouble understanding (and caring) about the complicated and indigestible tenets of Marxism.

“They [Russian industrial workers] found it difficult to take on board complex or abstract ideas, but they were receptive to propaganda in the form of simple pamphlet stories highlighting the exploitation of workers in their daily lives.” – Orlando Figes, A People’s Tragedy.

Class divide

And this clear class divide between bourgeois professional revolutionaries and revolutionary workers was not lost on the workers that the Bolsheviks – and wider socialist parties – would try to influence.

Working-class party worker Cecilia Bobrovskaya recalled in her Memoirs of a Rank-and-File Bolshevik with a vague sense of disapproval that Georgi Plekhanov, an early colleague of Lenin, was a “well-dressed, middle-aged European, clad in a light-grey suit, brown shoes and kid gloves.”

On her first meeting with Lenin, the seemingly breathless party member Bobrovskaya - herself the daughter of a lowly Jewish bookkeeper and illiterate mother - recalled in awe Lenin's simple clothes.

The future leader of the Soviet Union was in the early 1900s “dressed in an unbelted blue cotton Russian blouse.” In other words, Lenin is one of us – not one of them.

Faking it until you make it

Yet as is so common with revolutionaries across the world, bluff - or faking it until you make it – can be a powerful tool.

When Lenin was asked by a backer of Iskra, a revolutionary Marxist newspaper he would manage, on what authority he had to speak on behalf of the working class, Lenin answered:

"It [the working class] will become infused with the conviction that it already exists and that those are its sentiments and demands.” (Lenin and the Bolsheviks, by Philip Ulam.)

In other words, Lenin correctly predicted that the existence of a revolutionary movement comes across as a fait accompli if you’ve got a party newspaper.

Gaping paradox

As leader of the Bolsheviks, Lenin was well aware of the apparently gaping paradox: that the advocates of the small Russian working class were represented by a class of exploiters. Yet class divide isn’t the obstacle it initially seems.

“There was in Lenin's nature a strikingly practical side,” writes Ulam in the above-mentioned book. “The bourgeois intelligentsia were hateful, cowardly, and otherwise condemned; the worker was pure, courageous, and otherwise praiseworthy.”

“But when it came to the concrete problems of revolutionary organization… [ at the turn of the 1900s] it was ridiculous to think that one could dispense with the intellectuals. Where would a workers' party led solely by workers lead them?”

“Why, toward that spectre haunting revolutionary Marxism, trade unionism. For all his venom toward his own class Lenin was capable of brutal common sense. Karl Marx and Friedrich Engels, he wrote, came themselves from the middle class. A revolutionary party needed the intelligentsia, needed converts from every class.”

In other words, if your thinking was restrained for just better rights and less exploitation of workers, all you'd get would be powerful Western-style trade unions, which make for happier workers - but no revolution or change in system.

And if you can sense more than a spark of paternalism in Lenin’s thinking – that workers were in effect the noble savage that needed a push from the intelligentsia, you are not incorrect.

Not just a clever club

However, the Bolsheviks would not forever be the thinking man’s party.

Indeed, the Bolshevik party of 1903 was quite different from the Bolshevik party of 1917.

Later party leadership tended to come from more humble backgrounds – especially after Stalin (himself the son of poor peasants) - would purge most of the party’s bourgeoise founding fathers by the late 1930s.

All of Lenin’s Soviet successors: Stalin, Khrushchev, Brezhnev, Andropov, Chernenko and Gorbachev were all the sons of poor peasants and workers. You might argue that class-wise, this lowly line of succession was Lenin’s most on-point legacy.

Summary:

In summary, while it sounds simplistic, apart from an intellectual subsection of the bourgeois, most Russians at the turn of the twentieth century had neither the time, education, motivation, or funding to pursue revolutionary goals.

Lastly, you may observe that political activists and figures in more recent times come from somewhat similar backgrounds – but that would fall outside the scope of this answer.

Thank you for giving me the opportunity to talk about my passion!