1. It gives her a stable location that isn’t paradise island.
2. It isn’t a defined place like a real city so it gives writers and artist leeway in creating iconic locations within the city.
3. It can be used as a focusing point for All the magical heroes and villains in the DCU. Like Gotham is for street level heroes, and Metropolis is for more sci-fi themed characters. Gateway already has an association with magic thanks to the Spectre adding Wonderwoman to the mix would cement it as the Magic city.
4. DC needs a more marquee cities on the West cost To balance out the dominance of Metropolis and Gotham on the east coast.