Backup purge is not happening

I have two grav sites, both configured to keep a total of 30 backups. However, this setting does not seem to be honored, as one of my sites for example shows "Using 123 of 30 backup slots".

Backup storage purge trigger is set to "Maximum Number of Backups" and the "Maximum Number of Backups" is set to 30. The cron job is enabled and backups are obviously being created, they are just not being purged according to the count.

Please let me know what additional information I can provide to help troubleshoot this.