This used to frustrate me too, but gradually my position on the matter has shifted. There's a difference between really trying to solve some problem versus engaging in conversation with someone. I understand the temptation to insist on answering the question for real—which can almost certainly not be done in the moment—but generally, when you get into this situation of being asked a deep question in conversation, your interlocutor is not expecting you to actually solve the problem at hand; (best case scenario) they may just want to try working with you on it, or see how you would approach it, or (probably most common scenario) they just want to be recognized for having suggested the problem—or any number of other motivations. Point is, the motivation of actually seeking an answer is fairly uncommon. Honestly though, my tendency is still to try and answer it for real, but I at least think about this greater context for the question now (and at least sometimes treat the situation differently as a consequence).