I really can't imagine how a group can operate that many accounts. I think these are the work of freelancing training centres, where they teach students how to earn from Bitcointalk, and then they join the bounty campaigns and signature campaigns. Our country has many training centres where they teach how to earn from the internet and then let the students start working on various captcha typing and P.T.C. type websites. I wouldn't be surprised if the accounts belong to such an organization, where they operate these accounts as a large group. I think one person or two people can't operate that many accounts. I am not saying these groups belong to a specific country. But it's my personal opinion.
I never tried to catch anyone abusing bounty campaigns so the reason I found this farm was that multiple accounts post the same low quality style posts of 3 short lines and there is another one group which posts AI texts (they were spoiling the topics I was interested to talk that time). When you post something really pointless you can operate many accounts and if you hire someone to do the same work (which doesn't need to have any special skills) you can operate hundreds of accounts.
Some of found accounts are obviously stolen or secretly sold, I guess many of them. If to have time to dig deeper I guess there could be found many different violations. I found just few of them and just a part of this farm/s.