Re: Known Space; why so small??
The dtanceis only one aspect of the issue. Why would any spacefaring civilisation send vast numbers of its ships to the back of beyond? Only (if ever) when there was an advantage in doing so, whether economic, strategic or personal (which includes megalomania and "religious" beliefs). And double the distance travelled and the volume increases eight times. Even if there were some advantage, where would all the resources come from?
Let's face it, there are still odd pockets here on Earth (not including the barely visited deep ocean depths) which have yet to be explored. Why? Because it's worth no-one's while to do so.