Because it helps them move through the water faster.
Further information:
Penguins spend much of their time in the sea, which is their source of food. Flippers are needed to enable them to swim, in order to catch their food. Penguins' wing bones are fused straight, rather than angled like a flying bird's, and this has the effect of making the wing rigid and powerful, like a flipper. The small wings and a streamlined body shape are ideal for diving in water, and also give the penguin extra speed when swimming.
It is a flipper, which is a modified wing that penguins use to swim underwater.
Penguins.
You can call them wings, but they're more similar to a flipper. They certainly don't have wings in the same sense that flying birds do. Here's a diagram, which labels them as "flipper-like wings" http://www.enchantedlearning.com/subjects/birds/label/empenguin/answers.GIF
Flipper-Floppers
To hold its testicals
Penguins swim underwater to catch their food, such as fish and squid. Their streamlined bodies and flipper-like wings allow them to move efficiently through the water. Additionally, swimming helps penguins escape predators like seals.
Penguins have feathers, wings and a beak. Penguins lay eggs and feed their babies.
Yes, penguins are powerful swimmers and can swim long distances to find food. They use their flipper-like wings to propel themselves through the water at speeds of up to 15 miles per hour. Some species of penguins have been known to swim hundreds of miles in search of food.
Scientist think that both bird's wings and a seal's flipper have the same ancestors.
Penguins need to swim to catch their food, which mainly consists of fish and krill. Swimming also helps them escape predators and navigate efficiently in their marine environment. Penguins are highly adapted to swimming, with their streamlined bodies and flipper-like wings helping them move gracefully underwater.
Penguins have waterproof feathers that keep them insulated and buoyant in cold waters. Their streamlined bodies and flipper-like wings help them navigate through the water with precision. Specialized wing muscles allow them to "fly" underwater, and their thick layer of blubber provides extra insulation.
Penguins have adapted to be fast swimmers in order to catch fish, their primary food source. Their streamlined bodies and flipper-like wings help them navigate through the water with agility and speed. Additionally, being able to swim quickly helps penguins evade predators such as seals and orcas.