Why do ships use propellers instead of fishtail-like devices?

Why do ships use propellers instead of fishtail-like devices?

At present, there is a contradiction in bionic propulsion: if the mechanical design is more complex, that is, the closer to the fish tail, the more serious the energy loss is, and the more complex the control is. In the final analysis, bionic propulsion is not yet mature. I know that many of my colleagues in our laboratory are doing bionic propulsion, which shows that this thing can withstand theoretical deliberation, but has not yet found an excellent way. There may be bionic propulsion  ships in the future.