"Customer tags in Shopify are designed to help merchants organize and manage their customer data effectively. Here are a few reasons why tags are not automatically deleted from the system when they are removed from all customers:"
No one asked for tags to be automatically deleted. We should, however, be able to make the conscious decision to delete them and accept all reporting losses associated with deleting them, though. This is such a corporate non-answer.
"Shopify gives merchants more control over their tagging system" : If this was true then this thread would not exist.