SE doesn't ban accounts immediately, look back at FFXI task force. They try to find all accounts those bots are associated to and form a little web and mass ban as many of those accounts as possible together and at the same time. This eliminates their dirty currency and lowers the risk of them losing only 1 or 2 bots and being able to safe guard the Gil that they still have on any remaining accounts. Mass bans eliminate much more currency and make it a much larger investment to get back into the game.

It is much easier to dump 30 bucks into a copy of the game once a month because of a ban than to try and get back into it after you had 8 accounts banned in a single day this month.