I'm not a doctor but I belive the Black Death is bubonic plague, a bacterium. While yes that will evolve as well, the natural selection on bacteria happens on a very different time scale to a virus.

And hoping not to start a thread on antibiotics and superbugs, but bacteria do naturally select as well.

The Spanish Flu followed a similar path to Covid, it started deadly but then naturally selected to become less deadly. Its also somewhat unusual because of the numbers of displaced persons at the time returning home, the lack of basic medical knowledge etc.

But here's my point. The Spanish flu has mutated now to be basically Flu. It's not "deadly" anymore (for some definition of deadly). Non deadly mutations naturally select over deadly mutations.

It would depend on method of transmission. Bubonic plague was spread by rats. The hosts could be very ill or even dead; it didn’t matter.

Respiratory viruses that only or mainly have human hosts need ambulatory vectors.

Corona has other hosts, some of which seem to be unaffected by it.