Before scientists could confirm that this outbreak was indeed a new coronavirus, they called the disease COVID-19, which means COronaVIrus Disease from 2019 as it was discovered around November 2019 (some say September 2019). COVID-19 is the name of the disease, not the name of the virus. Since scientists were able to confirm this was really a new virus, the virus itself is called SARS-COV-2 because it causes Severe Acute Respiratory Syndrome.
So SARS-COV-2, the virus, causes the disease called COVID-19. Since COVID-19 was used earlier, it simply caught on with the general public and that is what the most common tag that is used on social media.
Source, the PDF from this page: https://www.fda.gov/regulatory-information/search-fda-guidance-documents/temporary-policy-regarding-nutrition-labeling-standard-menu-items-chain-restaurants-and-similar
