Because my style doesn't meet some requirements : no responsive, no jQuery and other JS libraries loaded and not based on the prosilver's layout (therefore a limited compatibility with extensions). Meet the criterions to validate my style isn't a priority. I've made Legacy for a specific website and I later decided to make it publicly available. It perfectly works for what it was designed for : a lightweight and retrocompatible interface.
That's a complety different project made by someone else. It was intended for phpBB 3.0 and the last version was released in 2013.
I've just added some screenshots in the first post, from the latest Legacy style.