yeah because they usually only have one babyyeah, but panda life is not sustainable. bamboo is a terrible source of nutrition, and they are giant, so they have to be constantly eating it. probobly because of this, they only look after one cub, even though they usually have twins. they just leave the other one to die. yeah, sloths and koalas are bad, but they can at least take care of offspring.
plus, Koalas are marsupians. When you have a pouch that does a lot of your childrearing for you, raising a baby becomes a lot easier. Sloth babies also just cling at their mothers. When your baby just clings to you and drinks some milk then and again, well that becomes quite easy
I still don't get why Pandas only eat bamboo. Like I get it, you lost your sense of umami, you don't like meat, but brown bears eat grass and other plant matter that's nutritious. Some brown bears have a diet of over 90% plant matter, yet they are super active, strong and smart. Why don't Pandas do that?
Other hot take:
natural selection by sexual preference can be very beneficial to a species. Example:
Female giraffes prefering male giraffes with longer necks have lead to one of the most dominant species in Africa. The long necks wouldn't have developed otherwise, if a giraffe just has a slighter longer neck, it wouldn't have much of a difference in their lifestyle. It needed generations upon generations for giraffes to gain the neck lenght to profit from otherwise unreachable foliage, immunity to ambushes and access to a massively powerful swipe with huge range
If such traits become too disadvantegous, the species will go extinct, but if not, it could evolve in a similar path to giraffes