I asked them one time a few months ago. they said they leave them open sometimes when they are running barnstormers and other leagues. not sure if any of those are going on now though.
One wonders why barnstormer leagues cannot have some kind of flag or start with something like barnstormers. Then they leave those alone. And delete everything else automatically after being empty for x number of days.
The fix they implemented was to delete all zero player leagues on a nightly script at about 8 pm PST. Sure a "flag" for Barnstormers leagues would be nice. Let's ask them for a flag then they will have more excuses why player ratings are being delayed.