Using Portal / Portal 2 as an example, the game doesn't put stress on you or force you to rush at any moment. Because of this, the player is more relaxed and able to enjoy what is happening around them, taking in the comedy and fully enjoying the storyline.
Compare this to an action game where the player is searching for collectibles, trying not to die, trying to shoot the bad guys, hiding behind something - it's all too much. There's too much of a stress on other things, that when a comedic moment does happen it's hidden behind gunfire and other worries that the player will have to deal with.
I'd also mention that it's hard to die in Portal, so you're unlikely to hear the same line more than once from any of the characters. In contrast it's usually fairly easy to die in adventure games if you're not paying attention, and to hear the same line more than once is death to comedic value. This can be linked to the fact that comedic moments usually happen at the start and end of a puzzle in Portal - this means you don't have to stop what you're doing in the middle of a puzzle to listen to the comedy.
Compare this to an action game where the player is searching for collectibles, trying not to die, trying to shoot the bad guys, hiding behind something - it's all too much. There's too much of a stress on other things, that when a comedic moment does happen it's hidden behind gunfire and other worries that the player will have to deal with.
I'd also mention that it's hard to die in Portal, so you're unlikely to hear the same line more than once from any of the characters. In contrast it's usually fairly easy to die in adventure games if you're not paying attention, and to hear the same line more than once is death to comedic value. This can be linked to the fact that comedic moments usually happen at the start and end of a puzzle in Portal - this means you don't have to stop what you're doing in the middle of a puzzle to listen to the comedy.