so again, why bother to go into the great unknown, when the other half of the galaxy is a large web of trade-routes and filled with allies.
Why did we bother to start eating meat when vegetables were sufficient? Why did we ever bother venturing out of the caves and build cities? Why did already wealthy European empires with well established trade routes between themselves bother going to America? Why does a millionaire want another million?
All I’m saying is that space is pretty big and scary, and when there’s so much nice stuff going on in one direction, the other might not be that desirable, especially not considering the civilizations they’ve encountered in that direction so far. I may have started out with an earth-example/analogy, but like I’ve said since, we’re dealing with a considerably larger scale here. And some pretty mean Rakatans, I might add. This is an EU map after all.
However, like I’ve more or less said before, if I had been given the task to draw a galaxy map for SW, I sure as hell wouldn’t have drawn it as they have. I’m simply saying that there is a logic to be found in the current design, especially when you start to look into the history they’ve added to it (I’ve posted links to the “history” of the galaxy’s exploration below).
Also if you skim through the wiki-article it seems like they’ve decided to put emphasis on the Rakatans, even having made it canon that they owned most of the galaxy at some point long before the Republic came around. So it seems that joefavs explanation was the right one; the Rakatans simply don’t want visitors in that direction.
The Rakatan empire (30000 - 25000 BBY); http://vignette2.wikia.nocookie.net/starwars/images/8/81/Rakatan_Empire_Atlas.jpg/revision/latest?cb=20090906172018
Post Rakata galaxy;
http://vignette2.wikia.nocookie.net/starwars/images/1/11/Atlas_pre-republic.jpg/revision/latest?cb=20101121120917
Galactic exploration (27,500 - 25 BBY);
http://vignette1.wikia.nocookie.net/starwars/images/a/a6/GalacticExplorations.jpg/revision/latest?cb=20090903055148
Alsakan conflict & Contispex’s Crusades (ca. 17000 - ca. 12000 BBY);
http://vignette1.wikia.nocookie.net/starwars/images/6/66/Alsakan_Conflicts_map.jpg/revision/latest?cb=20150825163745
http://vignette1.wikia.nocookie.net/starwars/images/9/99/Pius_Dea_Crusades.jpg/revision/latest?cb=20150816191635
The New Sith Wars (ca. 1000 BBY);
http://vignette4.wikia.nocookie.net/starwars/images/8/8f/New_Sith_Wars_map.jpg/revision/latest?cb=20151008122308
Early years of the Galactic Empire - Conquest of the Rim (19 - 17 BBY);
http://vignette1.wikia.nocookie.net/starwars/images/9/93/Reconquest_of_the_Rim.jpg/revision/latest?cb=20151029161051
The reasons for why half the galaxy remains unexplored may be convoluted, but it’s not illogical.
It’s just another over-the-top EU explanation of things, as evidenced by the fact that there was never any kind of map until about fifteen years ago. There wasn’t even that much of a demand for it until then. From what I’ve gathered from the wiki, most of this has to do with the lore of The Knights of the Old Republic games.