by M4stermage
As I understand it the encounter cards are mechanicly a timer/countdown for the scenario. Thematicly it represents the Castle and the dangers within to work against you because... Castle Ravenloft is a scary place.Even when the Villain/Boss is found, the timer/countdown continues and the Castle will give you no time to rest and deal with the Villain/Boss.
There is even a scenario (Adventure 2: Icon of Ravenloft) where you are required to draw an encounter no matter what (when you have found the Chapel). And this means you must draw one and additional encounter when not exploring, accelerating the Timer. Thematicly the Castle "knows" you are there and you want to steal the Icon and therefore it is trying to stop you.
One sidenote. Thematicly something has been strange to me when playing the game. Whenever you complete the goal of the adventure, the game ends...
When visualising this it seems odd to me. In the middle of the dungeon a quest is completed or Villain is defeated but does the Castle just give up? Do all creatures dissapear? I would think the party would not be safe untill they reached the exit... Maybe when Count Strahd was defeated the Castle would grow silent. But in any other case the Castle could still kill them, right?... Well, maybe that is just me. :D