Please note: this is NOT a request to change the reputation required to comment everywhere. Rather, this is a neutral support question asking about the existing limit.
I'm wondering why the minimum reputation required to make comments is set specifically to 50 reputation, and not some other number, like 10, 15, 25, or 100. I'm aware of the FAQ, Why do I need 50 reputation to comment? What can I do instead?. But that only explains why there is some sort of a rep hurdle, and not why the limit is set specifically to 50.
In particular, we already trust most users to not spam when they earn 10 reputation (the FAQ cites spam as a reason for the hurdle), and we trust users with 15 reputation to properly cast upvotes and moderator flags, and users with 20 reputation to properly talk in chat. 50 reputation seems like a rather large threshold compared to these.
Also, we've shown that many of the disadvantages outlined in that FAQ post are still gone even with a significantly lower limit, as here on Meta Stack Exchange, one only needs 5 reputation to comment.
Given all of that, why is the number 50 specifically chosen as the minimum reputation required to comment? I asked Shog9 in chat a while ago as to what originally motivated this specific number, and he responded that the limit has been in place since 2008, from before they kept firm logs of discussions. What is the current rationale for keeping the limit as is?