This is why it's relevant and I started looking into it. My landlord, flatmate, randos in the street etc started trying to pill me on the worst sort of conspiracy crap this year.
I'm going to write a bit about this, random thoughts.
What I think has happened is (see Simulacra and Simulation) people experience reality not through "raw reality" but through a web of symbols and meanings we've constructed to explain reality. When something new happens, we want an explanation of how that fits in with our preexisting web of meanings. Also, people don't like to feel powerless, they like the feeling of agency, even if that feeling is completely fake. It's the pretense of agency that is sought.
These two main facts explain why people are drawn to conspiracy theories in times of crisis. First, a crisis cuts through all the layers of meaning we've built up. For example, a virus kills a king as easily as a beggar or cuts across borders as if they don't exist. It renders our abstractions meaningless, so the layers of meaning are dissolved. Therefore a void of meaning appears, which is ripe for conspiracy grifters to exploit. The virus doesn't give a shit, there's no deeper meaning behind these events. Nature doesn't like us or hate us, it's a constant roll of the dice and this year we came up unlucky. 100 years worth of unlucky.
The main point here isn't that there are no other things that constantly challenge our beliefs, it's that a virus is just a harder one to ignore. So, a capitalist Christian can just ignore the homeless, because they rationalize away the existence of the homeless. Perhaps they're just bad people and God punished them for being bad.
The virus cuts through and challenges every belief system, however some face the challenge better than others. For example, if you have a good knowledge of science basics it's not that hard to follow along with the progress of the virus and nothing that's happening challenges anything we already knew about viruses and the risk of disease. However, for an evangelical protestant, for example, a pandemic is a serious challenge to their worldview, since if there's a Just God who carefully manipulates the world then it's hard to comprehend how a virus could just rip through and kill Christians and non-believers just as easily. So they're prone to conspiracy theories including that "satanists" caused the virus or are somehow manipulating the virus for power, because this absolves God of responsibility, thus reducing their own cognitive dissonance.
It's a basic test of how good your worldview was. If your understanding of raw reality itself was basically the same before the pandemic as afterwards, then by definition you had a robust world view. This doesn't mean it was right or wrong, but the pandemic is the challenge and if you can incorporate that new information into your worldview without having to change your understanding of reality itself, then your worldview was robust, by definition. However, people who have a worldview built on delusion, fantasy, no matter what book that's from, they're hit with the pure indiscriminate spread of a plague and suddenly they're yelling about how doctors are really satan and this has revealed that the servants of Moloch walk amongst us.
As for why they refuse to go along with health advice, that can partly be explained as wanting at least the illusion of agency. Going along with things like mask wearing doesn't feel like agency. For example, a local conspiracy theorist here was telling everyone to wear masks, back before it was general advice, but as soon as the government said they think everyone should wear a mask, she reversed her advice and said masks were evil. The simplest explanation is that by going against expert advice you can retain a feeling of personal agency, as if you're doing something about it. And even if this doesn't actually help you in the slightest, it helps these people psychologically.