The impression I got from the Rebels Recon on this episode is that they have limitations of what they can pull off for these space battles, and thus are more or less forced to limit the scope to an area of the planet or else they might overtax the computers. While it might make sense to have a planet wide blockade, they just don't have the processing ability to show it, so they take the shortcut allowed by the concept of pre-determined hyperspace routes.
There is only a few and sometimes only one safe way in or out of a star system via hyperspace. The Rebel ships can't really outrun the Imperials in Realspace, so they don't bother to attempt a cat and mouse game to try to break orbit and dodge around the star system until they can make a jump to hyperspace from someplace else. Because by the time they get someplace else, the Imperial turbolasers, ion cannons, tractor beams, and TIE Fighters should have managed to destroy the Rebel ships attempting such a thing. Any move the Rebels make from the surface, the Imperials can match, and the Empire almost always has the numerical advantage, especially if it has fully loaded Imperial Star Destroyers full of TIE Fighters.
There is only a few and sometimes only one safe way in or out of a star system via hyperspace. The Rebel ships can't really outrun the Imperials in Realspace, so they don't bother to attempt a cat and mouse game to try to break orbit and dodge around the star system until they can make a jump to hyperspace from someplace else. Because by the time they get someplace else, the Imperial turbolasers, ion cannons, tractor beams, and TIE Fighters should have managed to destroy the Rebel ships attempting such a thing. Any move the Rebels make from the surface, the Imperials can match, and the Empire almost always has the numerical advantage, especially if it has fully loaded Imperial Star Destroyers full of TIE Fighters.