Good module authors will allow for many possible options, but it's impossible for an author to think of everything -- that's why you need a DM.
And great module authors have set scenes up in a certain way that results in players who do what they think is the
smartest response to a scene... and that just happens to be the one the author has prepped for the DM ahead of time.
One of the issues it seems to me is that many folks here seem to just assume that their players aren't playing to the best of their ability. That their players aren't going to play smart. Which of course is always possible... but in my experience I think players
like feeling they are making the
smart decision. The
right decision for the scene at hand. They put 2 and 2 together and come up with 4... and they choose 4 as their next decision direction. And DMs and module can predict that pretty well. And thus the next scenes written and prepped are the ones that come out logically from the previous scene. If a location ends with the party finding a treasure map to a location 2 hexes away... it doesn't take a genius to guess the players are going to make a beeline to that location. A location the DM and module writer have graciously already prepared.
Now sure... there are some DMs who run the most open of sandbox games where every single adventure location is its own singular thing and players just wander across the open map in a random direction, find that location, finish that location, and nothing in that location prompts the players to go any further. And thus once the players finish it they just start wandering randomly across the map again until they find another singular location and do that thing (so on and so forth). So of course there's no logical progression to be had or to be made or to figure out, because every location is just a random event. With that kind of module, indeed there is no planning that can be made because the throughway is completely random.
(Of course, that being said... the fact that every location is a singular thing and there are no indicators in any of these locations to push or prompt the players to a specific next direction means that indeed the DM can
still create a linear path out of it by just not putting these locations on the map beforehand. Instead they just drop the next location they have material on into the map in whatever random direction the players wandered. If there's no story progression between locations, then there's nothing to determine what the next location is supposed to be. Which gives lie to the idea that sandboxes are inherently better than linear paths.)