I know this sounds odd but the real answer is they did not have a sure way to fuel the trip back. This presented a larger problem then people understand. They had some ships that where not in the harbor lucky actually at this time. If they ran out of fuel they where sitting ducks. They did also have ships at Mid way as well that had an angle to cut them off as well. These ships did haft the means to refuel in these waters.
Although this is some what a logical explanation it is was not the factor for them trying to make it the the coast. They could have just unloaded shells is the thing and returned delaying other action maybe.
Over all they well could have done other things but to hold things was another story.