I can see having different views but how come the majority of conspiracists tend to buy into every single conspiracy rather than a select few?

I am sure that there is a more appropriate term for this, but I don't know it so I'll call it the snowball magnet effect. Basically it hinges on the fact that for any ridiculous idea that might be imagined there is always someone gulible enough to believe in it. That's what the disinformation operations rely heavily on, they spread extreme theories that have sufficient credibility for ignorants to pick on and spread willingly, this helps make the theory more "believable" by the number of people behind it, luring more skeptics in, tricking more and more.

Disinformation operations such as: COINTELPRO, JTRIG, PSYOPS, MOCKINGBIRD, and more...

The main goal has always been to discredit a stereotype so that it can be used easily against dangerous dissent opinions by just labeling it or the voice a "conspiracy theory/theorist".

Most of the people that do not believe in conspiracy theories by now are already fully tricked on the idea that the majority of conspiracy theories/theorists = crazy talk/crazy people, all of this because that was and still is the result of such operations described before.

As evidence of this, your comment. You assume that the majority of conspiracists tend to buy into every single conspiracy rather than a select few instead of considering that that "majority" might actually be constituted solely by the snowball magnet effect + disinformation operations, which helps to discredit the few reasonable/logical theories by poor judgement association, for example: "Yeah? Well, most Nazis were german and since you are german then you are Nazi as well" or "Muslims are terrorists, you are muslim so you must be a terrorist" or "Don't listen to this guy, he is anti-semite" or "I don't care if Snowden helped the country see our true colors, he is a terrorist", "that journalist that exposed corruption believes in conspiracy theorists, I don't know how credible that makes him when he is a tin foil hat user..." etc.

EDIT: Wanted to add a better piece of information on this subject:

"Among the core self-identified purposes of JTRIG are two tactics: (1) to inject all sorts of false material onto the internet in order to destroy the reputation of its targets; and (2) to use social sciences and other techniques to manipulate online discourse and activism to generate outcomes it considers desirable. To see how extremist these programs are, just consider the tactics they boast of using to achieve those ends: “false flag operations” (posting material to the internet and falsely attributing it to someone else), fake victim blog posts (pretending to be a victim of the individual whose reputation they want to destroy), and posting “negative information” on various forums."

https://www.techdirt.com/articles/20140224/17054826340/new-snowden-doc-reveals-how-gchqnsa-use-internet-to-manipulate-deceive-destroy-reputations.shtml