because thats not what mRNA and normal cellular processes do and there is no mechanism in the body to allow that to happen. Reverse transcription only happens

because thats not what mRNA and normal cellular processes do and there is no mechanism in the body to allow that to happen. Reverse transcription only happens when a reverse transcriptase (found in retro-viruses, e.g. HIV-1, HIV-2, Hepatitis B Virus etc) does that and the RNA is the direct viral genome or a transcript of the viral DNA (for DNA viruses). They have special marker sequences at either end to facilitate this (search for terminal repeats) SARS-CoV-2 is not a retrovirus.