Why do I have more backups than I set in my backup retention settings? Why aren't they deleting themselves, and why do I keep getting more?
WHM's backup retention behavior, by default, will only count successful backups towards your backup retention limit. This means that failed backups will be retained until the next successful backup, putting the number of backups you have over the limit.
Enabling the strict retention enforcement option in WHM's backup configuration will change this behavior so that WHM will only keep the number of backups you specified, regardless if they are successful or not. However, strict retention enforcement will still keep one successful backup and will only delete it once another successful backup is created.
Here is more documentation on WHM's backup retention behavior: