First of all: this question is not about reasons for downvotes (although it implicitly refers to this).
The definition for votes on Stackoverflow is:
Good answers are voted up and rise to the top.
There is a guideline when asking a question what to consider (doing your homework, research first, choose right tags, etc..). But still this is not exactly making clear on which reason giving upvotes / downvotes.
This platform has plenty elaborated features but this one is still missing since I have seen lots of questions / answers which were down/up voted for unknown reasons, and especially lots of questions / answers with zero votes although it was a regular and certainly good contribution to this platform.
Why not giving a selection of references when to down/up vote the same way as guidelines asking / answering a question? In my opinion everybody would profit from that because things are getting more transparent.