In the book Treasure Island why didn't the Captain and his followers seize the ship while the crew was ashore?

The answer to this question is found in the very first paragraph of Chapter 16.  In this chapter, the doctor is the narrator.

He says that there were only six of the mutineers left on board and he and the captain and the squire could have overcome them and taken the ship back.  The only reason why they did not do this is because there was no wind.

The Hispaniola, of course, is a sailing ship.  If there's no wind, it won't go anywhere.  If they take the ship over and can't go anywhere, the other mutineers will just come right back to the ship and they (the captain and his followers) will be in trouble.