Account suspensions are typically handed out due to consistent and repeated disruptive behaviour, and then typically only after repeated warnings have gone unheeded. Their ability to answer questions well may factor in the decision, but disruptive behaviour cannot be entirely excused thereby (note also that the most egregiously disruptive examples are often cleaned up by community and/or moderators, so one cannot always judge how constructive a user is based entirely on what remains visible on-site).
From "A Day in the Penalty Box":
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 community.
- 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 everyone.
Stack Exchange sites are driven by community, and the best way to ensure that you don't get suspended is just to play well with the community. For the most part, just assuming good faith and following the general SE guidelines for user behaviour is sufficient:
- Be Honest
- Be Nice
- Avoid overt self-promotion