∞The first should be: No one knows exactly why economics are more important now than in the past. Remember the rule #12: Singular indefinite pronouns like "someone, anyone, each, neither, either (etc.)" take singular verbs.
∞In the second one, there's no wrong in there. It's correct.
Neither --> singular
debates --> plural
Why is it correct if there is 'debates' (which is plural)?
Simply, because 'neither' is the one we're talking about. Debates is the one that the 'neither' is talking about. (As I've said, neither is singular)
So, instead of was, we should put were.
Neither of the debates was successful <-- × wrong!