The setting of The Hobbit is intimately connected to its tone and plot developments. So when Bilbo moves out of his home territory and into foreign lands, the landscape gets dark, dreary, and cold. And when Bilbo and the dwarves are left on their own to face Mirkwood, suddenly the path starts to break apart. In other words, the way forward is no longer quite so clear. In The Hobbit, exploration is never just about finding new places for their own sake. Exploration is the only way for these characters to advance the plot of the novel. Any place that's outside of their immediate goals is literally left off the map.