Yes, the skin design itself is lovely, but why'd Janna get a slot in a trio of skins that are explicitly supposed to be about sacred sword wielders when the only time she even fully draws her sword is during her recall? All it does is act as an awkward stand-in for her staff 99% of the time.
Well in Janna's new lore she is an elemental spirit of air, and for most of her current skins are more focused on her elemental side, with the focus of Sacred Sword being, in my own opinion, trying to capture the more spiritual side of her character. Maybe the logic behind her having a sword is that she's really a spirit who inhabits the sword and her body is just a physical representation. I don't really know, that's just my thought.
To answer your question, she's the sword's protector. It's a SACRED sword, and I assume she's like a priestess. She taps into its magical energy to protect, which is supported in her gameplay, but she won't wield it as it is not for her to wield. I assume later, some destined hero (Shen) will receive it from her in some Lady of the Lake/King Arthur type deal.
Better question is why has every skin this year been Mythic or at least 1350 RP? Because Riot has more money to hire more talented artists ("more" of both quality and quantity) so now every skin is twice as expensive? The Worldbreaker skins are fancy, very different from their base champions in both style and concept and yet they were 750s while OS Tristana is basically just Buccaneer.
I could've even seen Beekeeper as a mythic or Legendary, its very nice and would've loved to get a new VO on it, but I literally cannot recall the last skin that was even 975 RP.
