Because you can swim faster and further with less effort, stress and strain! Compared to the conventional style fins that you probably own, the SplitFin operates more efficiently that the "paddle" type fins that you're used to. They deliver more propulsion with less drag and kick with less effort. Using hard kicking paddle fins can result in leg strain, fatigue and cramping. This reduces your ability to sustain high speeds for long periods of time. A fin that is hard to kick is often falsely perceived by divers to be an indication of power. However, tests with underwater speedometers show that these divers are often actually moving relatively slowly, even though they "feel" like they are moving fast. Kicking effort has no direct relationship to speed or power.
The Atomic Aquatics SplitFins virtually eliminate muscle strain, fatigue and cramping to enable you to swim longer distances against stronger currents. Divers have reported being able to make headway against currents they would not normally be able to overcome with paddle type fins.
Whatever the speed of the current is, you need to swim faster than the speed of the current to make headway. The true indication of power is actual speed. A small-range rapid flutter kick with the SplitFin delivers the same or greater speeds than any paddle fin without the strain.