5:46 AM
The question is two parts: 1. why can't users suggest edits on per-site metas, and 2. how to gain reputation, and therefore the privilege to edit, on per-site metas. The given duplicate answers 1, but not 2.
After a lot of searching I could not find a good post that covers 2 well. The only well-worded description is in the help center, which we can't close as dupes against. For this reason, I opted to answer with a quote.
I disagree with PolyGeo's stance that the question can be duped against a question that addresses only 1 because it asks about 1 and it should only ask about 2. Duplicate closures should address all (or at least a supermajority of) the question's parts.
As an alternative, if there's a good post that addresses 2 that I missed in my search, please add that to the duplicate list.