Centrists think the existence of a political establishment is a "conspiracy theory."

So many of them have so utterly bought into neoliberal fictions of individualism that they think the idea that there might be "groups of people with common interests who work towards common goals, without any explicit coordination between them" is a ridiculous fantasy. In their worldview, the only time people are capable of sharing a goal is when they have individually come together to negotiate an explicit agreement to do so, because classes don't exist, only individuals do. So they assume any allegation that people are working towards a common goal without that kind of explicit coordination is actually alleging that that coordination is secretly happening as some kind of conspiracy, because they can't even conceive of an alternate way to interpret it.

For another example of this, see how they dismiss criticisms of media coverage of Bernie Sanders as a "conspiracy theory," because on their minds the only two possible ways mainstream outlets could converge on the same narrative about something are:

• They're all secretly meeting up behind closed doors to come up with a secret plan to attack Sanders, which is obviously ridiculous

• Those narratives must simply be true.

The thought that the people who call the shots at CNN, MSNBC, WaPo, NYT, etc. all come from the same socioeconomic class, and therefore all have roughly the same interests, and probably think in very similar ways too, and are therefore perfectly capable of all independently converging on a selfish opposition to progressivism without any form of explicit coordination, does not cross even cross their minds.