why does sea diver wear special …

The atmospheric diving suit is rigid, strong enough to maintain normal air pressure inside against dozens of atmospheres of water pressure on the outside. The advantages are that the diver can breathe normal air instead of a special mixture, and can ascend and descend without special precautions, and can dive deeper and longer. However, a hard suit is significantly more expensive - perhaps fifty times as much - and generally out of reach of recreational divers. A dry suit or wetsuit, on the other hand, operates at ambient pressure (the same pressure inside and out) and is relatively lightweight and flexible.

Because deep beneath the ocean ,the pressure increases which can push the divers back to the water surface level.So they wear a special dress which can withstand the pressure and move swiftly.