Because there are so many Yin spirits, unlike Demon Beasts, when you defeat these Demon Beasts, you can still make up for the loss with their materials.
Moreover, these islands are rich in Yin energy. Even if you temporarily conquer them, they will continually attract Yin spirits from the sea.
Therefore, only some major forces, when needed, would occupy such islands.
But not all islands are suitable as bases for Sects or great families. For example, this island is too small to be valued by major forces, and small forces can't defend it.
Furthermore, it's deep within the Heaven-Reaching Mist Sea, where you're likely to encounter powerful Demon Beasts or attract a Yin Spirit Beast King.
So many cultivators wouldn't easily target these islands.
"However, for Yin spirits, this Blood Evil Red Sun Array of mine is also a nemesis."
