So, is an important being missed here? Was it COVID that killed off the flu strain, through some competetive effect, or the lockdowns? From memory the lockdowns where at least an important factor if not the major or only factor.
Seems pretty disingenuous to speak about this technically and not acknowledge at all that civil human actions can have such impactful public health effects as eradicating a virus, however "controversial" COVID lockdowns were/are.
The "bias" I bare here is that I lived through lockdowns which, multiple times, successfully eradicated COVID and allowed us to enjoy, in the middle of the pandemic and before vaccines, genuinely COVID free and open social activity without any need for masks etc. Only travelers from outside bringing in infections disturbed this and after a few lockdowns people clearly got over trying it. But having seen it first hand, a key lesson for me is that there is a version of human society, globally, that can completely handle novel viruses by deploying, amongst other measures no doubt, civil measures like lockdowns and completely eradicate them before they do anything like kill people, mutate and become permanent fixtures of human health and disease.