Do you know that cells replicate themselves by a process called mitosis, where it duplicates all of it's contents? This is how your body repairs itself, and it is very useful. Similarly, duplicated words are very useful in tags. As an example, it is useful when crediting artists that share the same first/last name. This improves both searchability and readability in the tags. (However did you know that brain cells don't duplicate themselves? I suspect you might not know as you probably only have 1 brain cell to begin with.)
Duplicated words are also useful when dealing with particles, as particles are often very common in the names of media that the song is tied to. As an example, with a vast majority of osu music being anime based, very long light novel titles often have repeat particles in english and japanese, so those duplicated tags help give these titles coherence. (unfortunately, it won't give your ideas any coherence at all since it seems you don't give them any thought anyway.)
Lastly, as others have mentioned, you not liking it isn't a valid concern for the ranking criteria. Unless you can find a reason that holds more weight, personal preference isn't good enough for judgement to be passed down on something like the ranking criteria. (For example, I personally don't like you, maybe even more so than you not liking duplicated tags. However my personal preference isn't enough for judgement to be passed down. If it were, I would propose a change that completely bars you from this game because you are either a troll or just really stupid, and your actions are a nuisance to the mapping and modding scene.)
Hope this helps explain why duplicated tags are perfectly acceptable and useful!