class solidarity.

no conspiracy needed at all. like how most people on welfare vote for higher payments and most of the middle class vote for tax cuts most of the wealthy 'donate' to both parties for favorable treatment (where do you think Trump got his billion or Biden got his 950 million for their respective campaigns?)

taken in aggregate it means that as a class the wealthy do indeed form what is effectively a single bloc on certain issues ie lower taxes, more corporate rights and power, more subsidies, access to captive markets like healthcare, energy, housing etc.

the easiest way to make more money as a billionaire is not innovation or invention its bribing both parties for favorable treatment (its why the list of the people who own 50% of global wealth gets shorter every year, they fight each other but they tag-team the people).

there is no conspiracy, these people are not friends or a cabal they just have massive power and influence and at that level the easiest ways to get more happen to be pretty much the same.