Database not backed up

I know there are some topics on this, like “Error backing up database”, but this is slightly different issue.

Most of my sites actually backup their database content to the sql folder, some sites present errors during this backup, which I ignore because of reasons. Some sites, however, neither give an error nor a backup.

Is there a reason for this? Is there a way to influence the decision-making-process for either of not backing up a database by Local?