i think multifactorial and all the rats eventually died out or something, due to reintroduction of especially terrier dogs/cats. also likely brown rats displaced the black rats.

The Black Death (bubonic plague) that devastated Europe and Asia in the 14th century did not occur on the American continent.

However, a later, separate outbreak of the bubonic plague was introduced to the Americas around 1900, resulting in the following recorded deaths:

United States (1900-1904): The first major outbreak in San Francisco killed at least 119 to 172 people.

United States (1900–2015): A total of 1,036 human plague cases were reported in the U.S. during this period.

United States (1900-1942): Before antibiotics, there were 511 cases, of which 336 were fatal (66% mortality rate).

United States (Recent): In recent decades, an average of seven human plague cases are reported in the U.S. each year. Centers for Disease Control and Prevention | CDC (.gov)

Key Facts on Plague in the Americas: Origin: The plague arrived in the US on rat-infested steamships from Asia, primarily affecting West Coast port cities.

Endemic Status: The disease established itself among wild rodents in the Western US (especially New Mexico, Arizona, California, and Colorado).

Location: While rare, modern plague cases in the Americas occur primarily in the United States and Peru. Smithsonian Magazine

I prefer people who survive the plague 🤷‍♂️

Technically, it didn't disappear at all!