Slowing Down Time on Starships
Intense gravitational fields and hyper-velocity have drawbacks... any collisions with debris and you're dead, no chance of repair. A slow boat might survive impacts, maybe even repair them. But gotta slow down time to shorten the trip. Can't think of any other way of doing it. Maybe someday when humans are mostly cybernetic organisms we'll be inherently able to do it.
There may even be several ways to achieving interstellar travel, but we haven't developed them yet.