Where I live we're concurrently experiencing, besides COVID19, a dengue fever outbreak. Dengue fever is spread by mosquitoes -- specifically, Aedes Aegypti.
Dengue is way more serious than COVID19. Particularly worrisome, having had dengue makes subsequent reinfections more life-threatening, not less.
There are ways to eradicate the mosquito -- mainly getting rid of small clear water containers near/within your home, such as vases and empty plant pots -- but we still don't do it until it's too late and becomes a problem. A single neighbor who doesn't do this endangers the whole block. And the authorities don't give a fuck. It's infuriating, really.
So to rephrase your question, why don't we do something about it? It's way more actionable than COVID19 (though lockdowns don't work for the reasons others told you). So who knows?