In the following I will I will use this example from one of your comments (slightly modified):
Question: Is Brazil an actual state?
Answer 1: Yes; it is recognised by the UN as such.
Answer 2: No, because of [wrong arguments].
Answer 3: It depends on how exactly you define state. […]
Answer 4: Argentina is an actual state; it is recognised by the UN as such.
Answer 5: We can probably better provide more helpful answers, if you elaborate why you think that Brazil may not be an actual state. Can you please edit your question to clarify?
Answer 6: Fish.
Answer 7: Yes, it is. Visit Brazil tomorrow with Spam Tours.
The general concept of Stack Overflow is that up- and downvotes cause correct and helpful answers float to the top and wrong and unhelpful answers to the bottom. As Adam Lear explained, wrong answers can still be useful as explicit statements that some approach is wrong or due to explanations given why it is wrong, e.g., arguing against the argument given in Answer 2 can be valuable to visitors who heard the same argument.
Most importantly, however, deletion (other than self-deletions) is mostly reserved for answers that live outside the upvote–downvote axis, either because they cannot be properly voted upon or because we do not want them regardless of their helpfulness or correctness. For example:
- Answer 4 answers a different question. It is correct (upvotish) but not useful for the asker of this question (downvotish). Also, if we kept such answers, Stack Exchange would turn into a forum or an unorganised heap of knowledge.
- Answer 5 should be a comment. It is useful (upvotish) but we certainly do not want it to be the first answer a visitor reads. It clearly does not belong into the answer domain.
- Answer 6 is nonsense: It could be downvoted into oblivion for being maximally unhelpful but in contrast to other wrong or unhelpful answers there is no benefit for visitors to know that or why it is wrong. It is just an entire waste of time to read.
- Answer 7 is spam. It contains an answer to the question, but even if this were the most useful answer, we would not want to keep it due to being spam.
Moreover, deletion (except self-deletion) should be reserved for exceptional cases¹ and misplaced content. In particular for good subjective questions and similar, it could be considered censoring if we deleted answers that we consider wrong. A high negative score on such answers should make it very clear to every visitor that the answer is problematic. Of course, an SE community can theoretically delete content as it wants (relevant XKCD), but on the other hand every user is free to consider the deletion to be too much. Though I have not made use of this, I want to be able to post a controversial answer (given that I do it in a civil way) and have it not deleted for that reason alone.
Relatedly, with not-an-answers, you can draw a line between deleting and keeping rather easily. With wrong and unhelpful answers you can’t: Who says whether an answer is so wrong, it should be deleted? If your answer to this is downvotes, where do you draw the line?
¹ except perhaps on sites such as Skeptics SE which have additional requirements for answers and thus receive more answers that do not fulfill them
