It should stay.
For one, I fail to see any problem mentioned. Messing with tags should be restricted to when there is a problem affecting their use.
For another, it helps signal the question is about the setting. Many people tag their general questions with the setting they’re in out of completeness.
Third, “lore” is a super non obvious tag and not something I’d come up with when asking my first Greyhawk question or whatever.
Fourth, as a devotee of campaign settings and not caring much about rules lawyering, it is a tag that tells me “you are probably going to be interested in this question.” I personally consider myself a "campaign setting expert" as I enjoy and have delved into the history and lore of Greyhawk, FR, Golarion, Eberron, etc.
Fifth, many smaller settings have less recognizable setting names and we don’t get many questions on them leading to disappearing tags for settings other than D&D settings.
It’s like every single other roll up tag. ‘Spells’ instead of just each individual spell. ‘Monsters.’ ‘Npcs.’ The tag conveys taxonomic value whether a D&D spell and an arms magica spell have anything to do with each other or not.