We don't want to encourage people to try to answer bad questions without enough information to determine an answer. We want questions without enough information to be closed, edited, sufficient information added, reopened, and then answered.
Answers that are just guessing wildly and that aren't at least reasonably confident in a solution are quite harmful on such questions. If you guess wrong then it makes it much harder for the question to be properly edited, as it is now invalidating answers. It also encourages people to continue to post low quality questions with little information, rather than encouraging people to provide enough information to provide a quality answer.