Short answer: because autocrats gonna autocrat.

Longer answer: I can only primarily speak about Nicholas II. Like his reactionary, hardline father, Alexander III, Nicholas II was committed to the principles of autocracy.

As the latest in a 300-year-old dynasty of absolute monarchs, and as a religious man, Nicholas II believed himself to be carrying out the principles of autocracy as per his role as 'god's man on earth.' In other words, Nicholas II viewed his role as something like a more executive version of the pope's.

However, Nicholas II was not without reason to believe he had a holy, paternal responsibility to the Russian empire.

As a young man, he had witnessed his own grandfather, the reformer Alexander II, torn to shreds by a bomb from a revolutionary group.

While massively simplifying the context, Nicholas II and his father Alexander III largely saw most reforms (at least those relating to democracy) as a bad thing, and ill-suited for the Russian people.

Fast-forward a decade, and Nicholas II's father, Alexander III died a couple months previously.

“Let all men know," Nicholas said in a 1895 speech in the then-capital St Petersburg, "that I, in dedicating all my strength to the welfare of the people, shall preserve the principle of Autocracy as firmly and unflinchingly as did my late father, of blessed memory.”

Strictly speaking, Nicholas II did preserve the principle of Autocracy as an attitude embodied in himself - but not for Russia.

Yet events were to force Nicholas' hand. A decade later, in the fallout from the disastrous Russo-Japanese War of 1905, which marked the first time in recent memory that minor power (Japan) knocked out a major one (Russia) Russia was gripped in its first revolution. Streets descended into chaos, with rioting and insubordination across wide parts of the empire.

'Rivers of blood'

For Nicholas, the revolution of 1905 marked a turning point - and an excruciating binary decision: 1) to crush the revolution with sheer military force and 'rivers of blood.' or 2) appease the people with civil rights, freedom of speech and press, and a Duma (or parliament) to check the Tsar's power.

Nicholas II initially opted for the first option - to crush the rebellion with the might of the empire. However, Nicholas's mind would change when the man he called in to the supress the rebellion, his soldier uncle, threatened to shoot himself on the spot with his pistol unless Nicholas granted a constitution.

Faced with that upsetting prospect, Nicholas reluctantly ordered the reforms - including the Duma which would check his power.

In response to the royal announcement, with the angry mobs appeased, the 1905 revolution subsided.

Royal backdoor

In theory, the Tsar was now a constitutional monarch, his power checked by an elected Duma. However, there was a royal backdoor built into the constitution which brought the Duma into law - the ability of the Tsar to dissolve the Duma at will.

Now, with the population pacified and appeased, Nicholas II saw a path back to power: through continued minimisation and rolling back on his reluctantly-granted reforms.

As he'd only allowed the Duma to exist under extreme circumstances, and couldn't risk another uprising by outlawing the Duma, Nicholas proceeded to do his best to stymie the Duma of elected officials at every opportunity.

Over the next eleven years, up to the final revolution of 1917, the Duma would be dissolved four times, and see five different chairmen. With no time to really get on top of its briefs, and met with obstinacy from the government it was supposed to help run and keep in check, the Duma would do very little of actual substance or worth - other than provide a legal platform for previously outlawed political parties.

One-man rule

Because the Tsar and his own state apparatus regarded the Duma as an annoyance at best, and a brood of vipers and usurpers at worst, Russia's political situation was the worst of all worlds. In Nicholas' mind, it was his Russia, and his to rule alone.

On the outbreak of the First World War in 1914, Russia did not benefit from either pure, unbridled and decisive autocracy, or participatory, collaborative democracy. In 1917, faced with no leverage or support from anyone with power - either his own army, decimated by the war; his government, largely by that time run by cronies and hangers-on; or the key urban populations who kept the factories running, Nicholas II was forced to abdicate.

He left the throne for his brother, Mikhail Alexandrovitch, who himself had little wish to rule, and even less support from the Duma, who believed Russia should instead be ruled by a more executive version of itself. Even before his abdication, Nicholas II had become a disregarded, antiquitated afterthought - forbidden to even return to the capital by insubordinate railway workers who blocked the royal train's path.

Dumas and Dominoes

Nicholas II was the wrong man at the wrong time - believing deeply in his own power and responsibility, but lacking the inspiration, foresight, talent and vision to see his will carried out.

A trivial, yet telling example of Nicholas II failure to grasp either the initiative or sense of reality of a situation is here: on 23 February 1917, as protests began to spiral in the streets of St Petersburg, the tsar, who was away managing the Russian war front (a mighty task he performed badly, as he'd only ever been a colonel, and was not skilled in military affairs), commented wistfully in a letter to this wife, the Empress: "I shall take up dominoes again in my spare time."

As Trotsky in his book The History of the Russian Revolution said of Nicholas II: "[his] ill-luck flowed from the contradictions between those old aims which he inherited from his ancestors and the new historic conditions in which he was placed."

Edited for spelling and minor tweaks.