That and they aren't really that awesome...Being able to zip around in the deep outskirts of a solar system where there is usually nothing isn't that exciting...
That being said, if you happen across one of the systems that does have a body of some sort way the heck out there you can get there right quick I guess. But it better be a nice planet. Full of high access high amount minerals. And many nubile nymphs. With grapes. This will justify the research cost. And the material cost. And the wealth outlay for all of the above plus the construction.
Coming soon to a theater near you in Aurora 6.3 or "Slave Women verses Hyperdrive Jim"