They go through a particular dungeon, clear it out to the point where they are satisfied, and then move on.
I can't really recall players ever backtracking very much. Maybe going back to talk to an ally or an NPC, but, even then, not very much.
Do your players come back to previously explored areas frequently?
My players are like this. They will clear an area and once they are satisfied with it, they move on. They will on occasion attempt to talk to certain NPCs in order to get aid, advice, or some other kind of assistance, but only if it paid off from the first interaction. Otherwise, they move on.
I think though as a DM, I probably don't provide them with enough incentive to backtrack. At least not without coming off as railroady.
If I was to create an adventure / campaign where I would encourage backtracking, I'd have several methods to state so such as:
1. In the campaign primer, I would advise the players that their characters may come to a dead end and that they will have to return to moment at a later time. The same with NPCs.
2. Create situations that become mysteries for the players to come back to. For example. The PC's explore Dungeon A and come across an area that they cannot get past. They move on because they accomplish the goal that was set out. Now, they go off to town B and come across an adventure which involves some study time in the library. While searching, they discover clues to get past the area in Dungeon A; however, they cannot decipher the clues just yet until they speak with Ye Olde Sage. They shelve the idea for now, because they also attend to the matter at hand. After their adventure, they go and visit Ye Olde Sage. Now we can either convulute this some more to where the PC's will have to backtrack to the sage or the sage helps out and sends them on their way. To avoid being railroady, the PC's will be able to accomplish whatever primary goal needs to be done.
3. Create a circular flowchart in the adventure. Location A leads to Location B which leads to Location C and that leads back to Location A. For example. Location A is the 1st level of a Dungeon which leads to Location B which is a ruined mine which leads to Location C which is a pirate's cove which leads back to the 1st level of the Dungeon which will now allow the PC's to get to level 2. Again, to avoid being railroady, create the locations which can be visited in any order.