Posts are hot and then become hotter by appearing in the sidebar. However, in small sites this initial hotness is difficult to get, so it is common that a debate never shows in the sidebar.
What criteria are used to select the links that appear in the community bulletin sidebar block? explains:
The rules are as follows:
- ...
- If there are still under four items, the rest of the space is filled with hot discussion questions not marked with any moderator status tag, scoring at least 3 and posted within the past two weeks. These are picked semi-randomly. (Note that the timing, score and tags can be adjusted per-site to suit the needs of each community).
In small sites, the problem comes with the scoring at least 3 and posted within the past two weeks part: it can be rare that a post reaches this score of 3, since not many users visit their Meta. So I would suggest allowing to decrease this number so it is easier for a post to make it to the sidebar. Some comments in the question should signal a debate, so they could be used as a parameter to take into account.