Perhaps their warp travel is more reliable because they, like the ancient Polynesians, know techniques and methods of wayfinding through the story realm of psychic energy.
Working together, clan fleets are able to navigate the warp with frightening accuracy and safety. It's slower then the imperium's punch through method, but they experience far less danger and can arrive at the destination with frightening accuracy.
Maybe even having the ability if they stumble on a route, to travel forward or backwards in time by going with that flow of the Immaterium. Of course it's hard to do, and incredibly risky, so it's almost never done.
They used to be an ancient small empire of nomads before the dark age of technology, trading with both Eldar and Humanity. However, when slaanesh formed, the warp became unnavigatabkr even for them, so they were forced to settle on a planet, and they soon abandoned their nomadic life style.
However when the imperium came, and began to exterminate their species, they once more took flight, the queen passing on the ancient knowledge of Warp Wayfinding to her daughter before she was killed and her people were broken apart.
A queen is required to unify their species, and the princesses know this. However he knowledge to create a queen was lost with their final queen, and thus the Princesses cannot unify their clans due to instinctual rivalries and grudges.
The Princesses are the only ones who can meet in person while being from separate clans without the meeting devolving to hostility and fighting, and they use this opportunity to try and guide their race. However, the needs of different clans and their differing situations lead to rivalries and bitter feelings, and the Princesses still hold the instinct to have their clan be dominate pushing them.
The way to make a new queen is to have there only be one princess remaining, but that would mean a civil war that would undoubtedly doom their species to extinction