Let's see if I can articulate this in a way that gets my meaning across.
The dungeon crawl is a style of play in which tense exploration is the primary mode of play. The situation, potential dangers, routes and occupants are all mysteries to be discovered. Explicitly, you can't predict what you'll find or run into because of the nature of the dungeon crawl: the place is ancient and weird and has been occupied and abandoned a hundred times over. It's unpredictable and in some cases nonsensical.
By contrast, the heist or B&E is not an exploration of the unknown. If it is, you failed to do your research before trying to pull off the job. Of course the unexpected might occur, but that isn't the point.
Does that make sense?