The answer is given in the first paragraph of that wisest, most insightful of tragi-comc novels - The Screwtape Letters, by CS Lewis (1942):
There are two equal and opposite errors into which our race can fall about the devils. One is to disbelieve in their existence. The other is to believe, and to feel an excessive and unhealthy interest in them. They themselves are equally pleased by both errors and hail a materialist or a magician with the same delight.
When we talk of true conspiracy theories and devils, we are talking of the same thing - the devils are the true, the ultimate, conspirators.
The commonest error is to believe they do not exist. This is a natural consequence of Modern Metaphysics - a set of basic assumptions concerning reality.
At bottom, when pushed, most modern people (and all of the Global Establishment, and nearly-all of the people close to them - the rules, those of great fame, wealth, status, power) believe that reality is a mixture of random and wholly determined.
(This is incoherent - which is how we know for sure that Modern Metaphysics is false. Nonetheless, it is what almost-everyone believes.)
In short - our standard, mainstream, near-universal metaphysics is nihilism - the assumption that nothing really matters.
Thus - the standard view - taught in schools, implicit in the mass media and all official discourse etc - is that there is no responsibility for anything; because either it is directly caused by something else, or else it 'just happens'.
From this angle, conspiracy is not possible, because there cannot be an origin for conspiracy. Either bad things happen by chance ('cock-up, not conspiracy'); or they happen because of long (and ultimately circular) chains of causation.
Determinism actually means that nobody or nothing really causes anything; because there is no origin of causes - everything is a cause and also a consequence of everything else: there is no uncaused origin.
Morally - everybody is a victim and an oppressor, both - just trapped in a web of causes.
There can be no conspiracy, because conspiracy requires agency; and mainstream metaphysics denies agency.
The other error Lewis described was to 'feel an excessive and unhealthy interest' in devils.
In terms of conspiracy theories; this means that people believe in devils but not God.
Probably this accounts for the mass of people who are interested in conspiracy theories. Their error is metaphysical - they believe in demons (or aliens) that are evil of intent; but they do not believe in the reality of God as ultimate creator, and as good.
So you get the mass of atheist conspiracy theorists, whose moral scale goes between evil demons/ aliens/ Illuminati at one extreme - and the masses of ordinary people at the other extreme; and the intention of the evil ones is to enslave and exploit the masses - probably also to torment the masses from sadistic pleasure.
The masses merely want to be 'left alone' to have a life of peace, prosperity, comfort, convenience, enjoyment and fun...
In the end, those with an 'excessive and unhealthy' interest in conspiracy theories, uncontextualised by an understanding of God, are merely hedonists. Their bottom-line, ultimate complaint is that the conspirators make most people more miserable... and the anti-conspiracy atheists want people to be happy.
That's about it! The global conspiracy aims to privilege the conspirators at the cost of reducing the average level of human happiness...
So, in the end it all devolves into wrangling about what socio-political System will provide the greatest pleasure and the least suffering - claim and counter-claim, evidence and refutation, assumptions of intention and denials... Their Establishment system is sub-optimal - but our Alternative system leads to a higher average gratification...
The wrangling never stops and vere advances; because who really knows which System leads to maximum gratification?
And, in the end, who really cares? By this account, we will all suffer and die, anyway; whatever the system. And plans for universal happiness (the 'utilitarian' project) always end by deciding who most matters, which person or group has priority. It always ends in a pleasure-grab by one 'worthy' group at the expense of another judged less-worthy...
So, in a world of atheism and hedonism, a world where people do not believe in causal agency; it is effective and substantially correct to label someone as a conspiracy theorist when they try to explain the Big Picture.
Effective because any explanation that tries to establish responsibility will fail in a world where the metaphysical assumptions are nihilistic. Substantially correct, because a world of devils without God makes no sense.
What does make sense is what is true: our world is the creation of God, who is good - and in this world there are real devils, demons and their servants - who conspire to oppose the goodness of God's creation.
The reality is Spiritual Warfare; and all true conspiracy theories are rooted in that reality.