The whole thing is kinda self explanatory, someone or group of users, could be bots nobody knows or maybe the moderators (handling the plagiarism reports) do know are reporting plagiarized posts in their numbers and as a result offenders are punished with permanent ban for regular users and other users who're considered as net positive and good for the forum are giving less punishment ( between 1-2years signature ban and 60days temporary ban).
The whole banning of accounts for plagiarism isn't new but the numbers of banned account had been on the raising in the last couple of weeks.