Is there a reason for this?
Probably so people wouldn't get embarrassed and have their heavily downvoted, downvoted again. It can be very annoying when users know that their worst questions are allowed to be viewed by everyone. People don't want that, and allowing negative vote questions will cause a revolt. I have bad questions myself and I don't want to share them with the rest of the world. So no thank you.
Is there a way to see negative vote questions with the new navigation?
You can see negative vote questions when viewing the
newest tab because these are the new questions that need to be viewed, answered, and whatever is needed to do with those questions. No matter what
show: is, you can see negative vote questions.
You might see it in the
need answer tab, but negative vote questions are rarely unanswered and most of time, already answered the second/minute it was posted.
You can only see it in the
popular tab if you downvote a 0 score question then click the logo. Then you will see the question which is now a negative vote question. But don't do that is not necessary...