Black panthers are not endangered because the term "black panther" is used for any black cat from a big cat species that is normally spotted. Black panthers are not a species on their own. Most black panthers are jaguars or leopards that have a condition called melanism.
Melanism occurs when an animal carries a variant on a coloration gene that makes the animal produce an abundance of black pigment. Black panthers still have markings, but they are obscured by the surrounding black fur except in strong sunlight.
Melanism is found in many species of cat and is often an advantage for them. In Asia, black panthers are associated with dense woodlands whose shade makes dark fur excellent camouflage; these black panthers are leopards. In the Americas, black panthers are usually jaguars, though other species of smaller cat may show similar coloration, such as bobcats. Melanism may offer some other advantages to cats besides camouflage, such as an improved immune system, though dark fur can also cause cats to stand out in well-lit habitats such as grasslands.