The society is depicted (outright stated even) to have regressed socially, culturally and technologically from our own past. They are technologically inferior to the co-dominium, but they have also reverted to an outright medieval societal structure including women being babymakers and not much else. It's not the authors saying that's how things should be, nor is it the authors writing that way because they didn't know any better (it was written in 1974, so they're part of that wave of brilliant SF that was coming out during and after the height of the counterculture movements). It's just one of the worldbuilding things. It's a less extreme version of what you see in Warhammer 40,000, actually.
The Moties are one of the most interesting SF species I've read. It's not that they are alien in every single way, but Niven and Pournelle successfully built an alien psychology without simply resorting to "oh, they're like ants!" or "they're like humans, but super greedy!" There are moments of familiarity where you can see examples of convergent properties, but you also see the long, ingrained influence of their cyclic and ancient history carving its mark on the way they think, act and organize their societies. There are reasons for the way they are, they're not 2d cutouts and they are sufficiently different from humans as to satisfy verisimilitude, if they are not actually "realistic" in the strictest sense of the word. There is a mystery to the way they behave, but the few occasions we get to see inside their head we can see that they are just not quite the same as we are, and they take such a different perspective on so many things.