Coronavirus extinct in Japan due to too many mutations? Scientifically unlikely

Japan went from being one of the worst affected states by Covid19 last summer to having virtually zero cases in the fall. Some Japanese scientists have speculated that the virus committed suicide or ‘self-extinguished’. What could push an infectious virus like Sars-CoV2 to self-extinguish? According to the Japanese researchers, an uncontrolled number of mutations would have led to the so-called mutational collapse, from the English ‘mutational meltdown’.