|Chad Brown Pathfinder Adventure Card Game Developer|
Imagine there are 2 players and 4 locations, where both players begin at the same location. On the first player's turn they decide to move to another location and player 2 decides to stay. Now both players are on different locations. Player 1 ends their turn and now player 2 begins their turn......piloting the ship? That is ... weird.
Don't think of it as "piloting" the ship. On each character's turn, they are commanding the ship - that is, they are giving the orders, and the crew of the ship are carrying out those orders. A typical ship will have more crew than even the largest PACg game, and they're busy doing crew/ship things, not adventurer/exploration things. These things include sailing from location to location between turns.
This is also why many of the Task barriers let characters use as many allies as they have at hand - those specific barriers are the sorts of things where you benefit from having as many people as possible helping. Put another way: you don't want 6 people navigating, because no matter how many courses you get from those 6 people, the ship can only go in one direction. If you're swabbing the decks, though, the more the merrier (or at least, more effective-ier).
So essentially the ships during movement only allow for extra movement on other players turns if you are in the same location an active player is when they move, you can move with them ... and that is it? Did I get that right?
All ships have a power that they give to the commander, and they collect plunder. They also allow the commander to bring characters along when they move. They don't allow characters at other locations to move anywhere, because those people aren't where the ship is. If you want to know why you can't "swing by and pick people up", the answer is "the same reason that you can't do that in RotR without a ship." During your turn you don't have time to run grab other people on your way hither and fro -- unless you do, in which case a power will tell you that you do.