If your world has multiple people species, why?

It's common in fantasy and sci-fi to have multiple distinct sapient species (races). How did all of yours come about and survive to the present day without any one species becoming dominant while the rest went the way of archaic humans?

My world doesn't have any moon or stars, so keeping track of seasons is a lot harder. That makes agriculture really hard, so populations are only as big as can be supported by hunting, fishing, and gathering. This means everyone had more time to evolve and develop sapience and cultures. Still, that's only 5 people species for me, one of which is extinct and another of which is a kind of plant.