Can't speak for MR, but I moderate on two other boards, and in each case we reach decisions through collective discussion. Unless it's a clear case of spam, no one moderator can make a decision on his/her own. In many cases it's black and white and the mods will be in immediate agreement, but in some situations we'll have dozens of posts between us before a decision is made. Point is, there is enough nuance in moderation to warrant discussion before decisions are made, and even if an AI were capable of such nuance, I wouldn't want a single source making the call.