Considering the information moderators see when other flags are used, why aren't they able to see who flagged a post as spam?
It would be helpful when there are many flags that need to be handled, and moderators want to first handle the secure ones. If I would see a post has flagged from a user who keeps flagging as spam posts simply because they contain a link, or who keeps flagging posts without a good reason, I would handle the flags from that user as last step.
Probably, this is relevant on sites smaller than Stack Overflow. I saw what I considered spam posts only in few cases, on Stack Overflow, and I guess that most of the spam is not handled by moderators.