Naturally no world can be as big as... well an entire world... That'd take far to much resources and developer time to build out every facet. Also it'd take load times EVEN longer.
Walls are great in terms of development practices as they allow great use of occlusion mapping, which will reduce an area's draw calls.. So unless you want more performance drops issues and what have you, be thankful we have something to break up the environments a tad.
As the engine progressions and SWTOR grows I'm certain we'll see more expansive landscapes.