I feel like maybe it's because conspiracy theorists have a tendency to distrust authority/science. And the global authorities/experts on the matter of covid-19 have been kind of all over the place. There's been all this changing of information, differing of opinions, and some unfortunate misdirection from some of the leading authorities on the matter. Not to mention the bone headed crap that some politicians are spewing out. And I think instead of wading through all of that to find the reputable information, it's easier for a lot of people to subscribe to a conspiracy mentality. Especially if they already have a bias against science/authority/government etc.

It's the same as the people who are anti-vax, or believe in a flat earth, or believe in aliens. Now that the global community has started to settle on the facts of covid, the conspiracy theorists want to refute those facts. We debunked the theory that vaccines cause autism, yet people still fear that vaccines will hurt you. We have loads of information to prove that the earth is round, yet people still believe it's a huge conspiracy run by NASA. We have no real, tangible evidence to believe the earth has ever been visited by aliens, yet people still see UFO's in the sky and think it's a government cover up.

It's the same with covid. The government wants us to wear masks? But just a couple months ago we were told not to wear masks! What's going on??! Obviously this is a huge conspiracy. /S.

That's my take on it anyway.