I don't have a lot of experience with bli$$ard's bans, but I strongly suspect that most of them happen due to datamining, not because a bot is actually detected.
If you look at the hellbuddy bot, their bot technically isn't detected and although many members have been banned there are still a huge number that haven't. If the bot were actually detected a good majority of them should have received bans.
The bans most likely are due to people using the same script for 20 hours a day or simply botting 24/7. I can't say for sure, but a lot of the scripts that may have become outdated from a patch may be dangerous to use as well. I know I used one that was messed up for some reason and it would just disconnect with an error message, remake the game, disconnect again, and reconnect over and over again, which seems like activity that may get you flagged. I've heard of another player using a script on a brand new character botting the act 1-1 quest before you received the town teleport, and the bot would use tp anyways, and he got banned with less than 15 hours of playtime on the account.
Yeah, it makes sense. And the hellbuddy mods had virtually zero bans, and I know they were running their bots with little trouble compared to the average user.