What does redundant matter in terms of tags though? Isn't it a good thing to find a story via multiple avenues? Because if I want to find, say, Kusari wa mou Iranai, what do I search under? It's got an office lady in it, but the protagonist is a manager. Doesn't it make sense to search both ways?
There's simply a larger audience. Your average yuri reader would rather have a story featuring teenage girls rather than one featuring adult women.
And that's why we can't have nice things.
Note that we're talking about the average viewer in Japan. Plus it's easier to pass off yuri under the figleaf of Class S over there, rather than have characters be overtly gay like with Adult life material. Not to mention the whole Japanese fondness about stories about youth, and you don't get much more youth than middle school.