The Colony of Sigma Draconis

The idea of these structures came to my mind when reading about the vast amount of mineral resources in the bottom of the ocean. I thought that in order to have easy access to those resources this kind of structure could perhaps be more practical than completely underwater structures, which is what we typically see in movies and books. In these structures it's much easier to get in and out, for example. No need to take a submarine to go to work, just fly into the city. People would actually have the benefits of living underwater with the benefits of direct contact with the atmosphere and sunlight. So, why not have a complete mining city in this way? Or even a multitude of them?