Among radicals - both on the mainstream left and on the 'secular right' (which is actually just a branch of the secular left) - it is normal, and regarded as sophisticated, to explain everything large scale than happens in the world as a result of economic motivations.
It is surprising that the mainstream 'right' should go in for this, since it is so obviously a Marx-derived practise - but it is true.
Indeed, this delusion affects almost everyone when trying to explain something they don't like - i.e the perpetrators are accused of monetary greed: greedy bankers, developers, capitalists, trades unions, politicians, feminists, antiracists, social justice warriors... all are often accused by their enemies of lining their nests, of being covertly and primarily motivated by economic advantage.
At times this reaches the point of absurdity - Western politicians who are destroying their economies with mass unrestricted immigration are accused of seeking economic advantage. Of course, there is always an advantage for a few even in a mass collapse; what is happening is that the unit of analysis is continually being redefined and narrowed (salami sliced) until someone can be found who has an economic advantage (whether short-, medium- or long-term)... and then that is accepted as the explanations.
Indeed, most analysis does not seem happy until it has reached this point: i.e. an explanation in terms of greed for money.
But the idea that economic factors are the bottom line explanation for human behaviour is very recent, artificial, and abstract. By contrast, the idea that some people are motivated by evil is ancient, spontaneous and concrete. (Think of fairy tales and myths.)
But - since evil is defined in relation to its hostility to good (Subversion, Destruction or Inversion of Good) - then evil does require that the arguer acknowledge the reality of Good.
And this is the problem. Secular people (and indeed many religious people) have trouble believing in the reality of evil as a primary explanation in human affairs, because they have trouble believing in Good. They regard Good as merely subjective, a point of view - therefore they cannot imagine that the motivation to attack it could be a powerful factor in Life.
There are at least seven 'deadly sins' traditionally recognised, and avarice is only one of them!
The Establishment, the global conspiracy, are indeed very rich indeed; but they are not rich because they are evil, their evil being a means to the end of wealth... The truth is most worse. The truth is that they are rich in order to do more evil: their vast wealth is a means to the end of subverting, destroying and (especially) inverting Good.
Maybe that is another factor behind the assumption of bottom-line economic motivations: the truth is so much scarier.