The accomplishment of Sabine Pass was not to break the blockade of Galveston (which, by the way, remained a haven for blockade runners to the end of the war). It was to thwart the attempt of The Lincoln to seize east Texas' cotton stores, the so-called "breadbasket of the confederacy" during the war. The dissolution of foreign trade and the war had left the north short on cotton and in economic chaos in those industries. That cotton was in east Texas, unimpeded by the war, and The Lincoln set out to get it. His mission was of two purposes - get the cotton for the north, and in doing so take from the south what it had been running through the blockades for its own sustanence.
Sabine Pass thwarted this mission, forcing The Lincoln to try again. The next try was called the Red River campaign. He put together a 45,000 man invasion force along with 58 warships - the largest inland fleet ever assembled on the North American continent. He sent them to invade from northern Louisiana. They were thwarted again at Mansfield.
'Breadbasket of the confederacy'? Did they eat the stuff?
That cotton was in east Texas, unimpeded by the war, and The Lincoln set out to get it.
That can hardly be the reason since there wasn't much of it. In the year prior to the war of the 3 million bales of cotton exported from the south only 68,000 came through Galveston. Not enough to make a dent in the Northern demand. If the purpose was to get cotton it made more sense to go where the cotton was, in Alabama and Mississippi and South Carolina, instead of Texas where the cotton wasn't.
Because of the blockade what traffic there was out of the Galveston area tended to be one way - during some periods over 80% of the ships which left never returned, either with cargo or to pick up another load. By the time of Sabine Pass Vicksburg had fallen and the Mississippi was cut so nothing in the area could make its way east. The Texas authorities were looking more towards Matamoras as a port rather than the useless Galveston area. So Sabine Pass was a minor sideshow of the war, an embarassment for the Union commander, perhaps, but nothing more. It didn't delay the outcome of the war by a single day.