There are 64 servers in total (might have miscounted, correct me if I'm wrong) and just as a statement there are about 5m registered accounts. Let's take this into a theoretical calculation and say about 10% of the accounts are bots/gil spammers. That's 500,000 accounts, roaming endlessly throughout 64 servers.
To observe and report all 64 servers and find the odd cases will take a tremendous amount of time and resources. Even if there is a central data server that monitors all the data that goes on in every server, that still means there will be billions of coded data passing every minute.
Also, not everyone who looks like a bot is a bot. For example, I myself went out and farmed wool way back sometime during 2.0 from Karakuls. I would spend on average 4 hours a day about 2-3 times a week just endlessly farming. Does that make me a bot? No.
Every case needs to be examined, it might just be a person who is really determined to farm, who knows.