Well I mean it depends on the "dungeon", right? If you're passing through the gatehouse of a ruined fortress, "randomly in the middle of high-traffic halls" is exactly where you'd put your traps, because the original builders would've wanted to create killzones right where invaders would go. However, most of them would've already been set off by whomever did the ruining. (A spiked pit with its cover collapsed is still a spiked pit, though.) On the other hand, a royal grave might have traps concentrated near the entrance, since any point beyond that the grave's already been desecrated. A paranoid noble would have traps guarding their prized possessions, but with mechanisms to disable them. Can't count your gold if you can't get to it.