I think it is a combination of things including the very real health impact of a psyop launched against the people of the world.
However, I have found Jon Rappoport's take on things very helpful. In industrial settings illnesses (especially respiratory!) are caused by toxic exposures (think small particulate air pollution) for which an employer could credibly be blamed. So…manufacture an infectious health crisis to divert attention, belief and blame away from the toxic polluters. This is corroborated by Dr. Zach Bush who said that "COVID" hot spots line up with areas experiencing a lot of industrial pollution.
Once you have people believing that there is a VIRAL infection to blame you can introduce all sorts of illness causing substances and pathogens to keep them getting sick. I have found it more than curious that a number of the top useful therapeutics are used, generally, to treat parasites, especially intracellular ones, instead of "viruses".
I think you can consider mycoplasma, bacteria, cyanide poisoning, 5G, legionnaire's disease, and various "viral" agents as "causes" for the very non-specific, mostly meaningless conjunction of symptoms falsely labelled "COVID-19".
If you search for "Operation OpenScript" you will (I hope) still be able to find information about the apparently very sloppy US bioweapons development programs. Think Plum Island research and the site of origin of "Lyme disease".
A point to note. A lot of vaccines are loaded with aluminum. Aluminum can reportedly cause bacteria to lose their cell walls and enable them to become intracellular parasites. We are also barraged with aluminum in consumer products, cookware, etc. Most toxic though, to get it via injection.
We should all be wondering why HCQ treats an intracellular parasite and is helpful in cases of LUPUS (auto-immune disease). Could at least some cases of "auto-immune" disease be the body's attempt to rid itself of pathogens that have gone intracellular. Vaccines do not necessarily prevent infection, they may be masking symptoms and causing new illnesses.