Purge or hide groups reduce to spam traps
It's completely understandable that Yahoo would want to try to sue spammers for messages posted in the various groups, so Yahoo should at least hide groups until they're done with their lawsuits.
Otherwise, groups reduced to spam traps are likely abandoned by their owners and members and should thus be deleted.
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And yet group creators don't seem to think about closing such groups.
you've got that backwards. Moderators don't leave because a group is a spamhaven, it becomes a spamhaven because the mods stop moderating.