If you follow the link, you will get to this blog post from 2009 which explains this in-depth:
Our general strategy is to discourage specific problem behaviors, not
individual users. But sometimes you just can’t seem to reach people,
and it becomes necessary to place accounts in timed suspension.
When users exhibit a pattern of either …
No effort to learn and improve over time
This user does not put reasonable effort into the questions they ask of the community.
There is little or no evidence of this user learning over time, either in the topic itself or in the community norms on the site.
This user intentionally spams the site with the same question or very similar questions, over and over.
The user never gives anything back to the community, but only takes.
Other users tend to react poorly to this user’s contributions, posting negative responses in kind and generally causing a commotion.
There is a broad sense of community resentment over this user’s behavior, and they are frequently cited in discussion about the
There is a dark storm cloud of moderator flags that seems to follow this user around wherever they go.
The moderators get email complaints about this user’s behavior.
This user makes overtly snide, rude, or hostile comments to their fellow users.
… these problem behaviors have to be dealt with. When they aren’t, it
takes up excessive moderator time that could be used for something
more productive — and, even worse, these behaviors begin to actively
turn people away from our community, stunting its growth and harming
To me, it seems that the criteria are purposefully broad. Any repeated behavior that hurts the community can result in a temporary ban. This obviously goes for abusive posts, but can also result from a large number of low quality posts which may not result in a ban on their own (example).