No, is not about a large variety of cuts and styles. They became well known because their pants, while generally on the slim side, don't make you look like a hipster in skinny jeans, but they also don't look like parachute pants. In the US, mass market men's pants tend to be really baggy and unflattering (aka "diaper butt") for anyone with a slim or athletic build, and that was the niche Bonobos filled.

In short, their pants just make your butt look good.