Well, I mean, the whole "Oh yes-- a monster that gets off on forcing mortals to answer stupid riddles, and eats them when they screw up-- YES! Let's TOTALLY just allow this thing to keep doing that! THat sounds like a GREAT idea!" is something that should not be overlooked in the motivational rationale of a character. Playing along with the stupid game the monster is engaging in would require a specific alignment with lawfulness (Following the rules as provided, VS being a rule breaker and refusing them), and would require either a neutral or evil alignment on the good axis, for the PC to really feel good about getting through the puzzle by answering the question, as opposed to just offing the damn monster and doing the world a favor, or die trying.
A barbarian that has been around the block a few times could very well be jaded as shit about things like that, and really-- just not want to even try playing the game-- Will see the damned sphinx guarding the gate, and be like "Fuck answering his shitty riddles. You know what? Wizard guy-- I want you to buff your luck right now, then precharge hold monsters at the strongest level you have, and you, Mr Rogue, I want you to get that crazy rope you have ready-- We are gonna walk in nonchalantly, and when it asks us about its stupid assed riddle, we are gonna give it the choice of having its shit fucked up, or fucking off and letting us past-- and depending on which it chooses, that is what it is gonna get-- Game?"
It isn't something so innately tied to their wis or cha-- it has to do with their personality, backstory, and personal ethos. They could be totally eloquent when dealing with humanoids, for instance-- but be total assholes to smart-assed monsters who act like they wont get their asses handed to them.