Because of its high salinity. The salt content of the Dead Sea is an increadibly 342 g/kg or 34.2%. Over a third of its mass is salt. The Dead Sea is actually a hypersaline lake instead of a sea. (By the same token, the Caspian Sea is also technically a lake.)
The Dead Sea has an extremely high salt content because the waters of the Jordan river and a number of smaller streams flow into it but it has no outflows. The outflows are missing because the lake surface level is kept in check by the very strong evaporation typical of the climate zone that it is in. The rift valley in which the Dead Sea is located forms part of the border between Israel and Jordan at 31 degrees north. The lake is in the desert belt to the north of the tropics with little rain, low air humidity and powerful sunshine during most of the year.
Interestingly, swimming in the Dead Sea is very different from swimming in even the ocean. That's because the density of the water is 1.24 kg/l or about 24% higher than sweet water. Below is a link to a video of some guys swimming and floating in the lake. It's incredible how different it is. It's almost like lying on your back on an air mattress making it possible to read a newspaper without the paper getting wet.
The dead sea is the most minimal point on the Earth, and its shores and surface is really at 430.5 meters (1,412 ft) beneath ocean level. How about we see why it is
really named the 'dead sea'. Dead sea isn't generally an 'ocean' it is a salt lake circumscribed by Jordan toward the east and Israel and Palestine toward the west. The
dead sea is 10 times saltier than the typical sea water that no life can get by in the water, giving it the name 'Dead sea'. Anybody can without much of a stretch buoy
in the Dead sea in light of the higher thickness because of the salt substance. The water and the mud at the shores has numerous therapeutic qualities however.
With its world record of salinity, one might think the Dead Sea an environment hostile to life. Nevertheless, this salt lake is home to many life forms: unicellular organisms and algae.
It may well reach a record of salinity (275 g / l, or about 48 spoons of salt per liter of water!), It does not completely prohibit life from developing there. This 810 km2 stretch of water wedged between Israel, Palestine and Jordan is in fact a salt lake, not connected to the sea.
For nearly seventy years, the area has been subject to the turmoil of the Arab-Israeli conflict. But none of the belligerents are responsible for the state of the Dead Sea. It is an excess of salt that seems to have caused this geological murder perpetuated well before the age of medical examiners.With 27.5% of salt, the water of this sea beats with a considerable margin the average salinity of the water bodies of its species: about 2% to 4%. The number alone makes the hypertensives nervous. Fish and seaweed, they can not survive in this environment saltier than an addition in a caviar restaurant, and it is their absence that justifies its name of "Dead Sea". The investigation is still going on, with a few hundred thousand years behind schedule. The sea itself is not as innocent as it seems: it is in fact a lake, and this usurpation of identity is suspect.
Because uf its high salinity. Almost nothing can live in it. Also due to the high salt content almost everything floats. Humans can float in the dead sea much easier then in fresh water.
How Dead Sea got its name
Your average sea will contain about 4% salt. The "Dead sea" which is actually a salt lake, contains 29% salt. All that salinity prevents any life-form from establishing its ground anywhere near it. That's why there are no fish, flora or fauna around it. Giving it an appearance of death surrounding it. Thats why the salt lake is appropriately named "The Dead sea".