Just money grabbing opportunities. Currently, the vitamines are in high demand, so they can sell them at higher prices and sell them more, since a lot of people think they are miracle cures. And people who support them would rather buy those vitamines from them and at higher prices too, to even support them financially.
There are a lot of people who are just looking to cash in on current situations. Like when 5G was starting to be introduced, and uneducated consiracy theorists starting making various claims, scaring people. A lot of people jumped on that bandwagon and started selling ridiculous products that where supposed to protect you from "lethal G radiation".