[Sayrus]

I'd imagine there are monetary incentives to having many accounts able to boost you and keep your post on the front page. Doing that with brand new accounts who have no comments and no karma is probably harder. In the cases listed, all the comments were heavily downvoted but there are other bots out there who have a positive karma.

[defrost]

FWiW this network slid in unnoticed and unflagged in the past 20 days until someone noticed and pointed them out.

eg: https://news.ycombinator.com/item?id=41024612 (9 days ago)

Since then they're mostly rapidly auto-flagged.