What do they base this on? What do they know about how coronaviruses come and go?
Here is what they do "know":
1. The medical community at large doesn't really know much about this virus. It has a ton of unanswered and unexplained questions and phenomena related to it. That same community initially made fatal mistakes in treating covid-19 patients.
2. A huge percentage of their community was exposed to the virus. Tests are only partially reliable. It clearly seems that those that got it aren't getting sick a second time (at least this season), and for most people contracting the virus isn't fatal.
3. They see facts and outcomes. Whether the "scientific medical community" agrees with premises underlying those treatments or not, they trust their senses. That is why those same communities will trust and embrace alternative treatments for a variety of issues, even if practitioners won't present establishment accepted credentials.