Because when one name is used to identify someone you do not personally know, the convention has long been to use their surname.

Hence we say:


  Shakespeare wrote The Tempest. Churchill was prime minister of the UK when it was at war with Hitler. Washington was the first president of the US. Einstein developed the theory of relativity. Shelley wrote Frankenstein.


Not:


  William wrote The Tempest. Winston was prime minister of the UK when it was at war with Adolf. George was the the first president of the US. Albert developed the theory of relativity. Mary wrote Frankenstein.


Among other things, the most common first names are probably more common than the most common surnames:


  John was the last US president to get fatally shot. John wrote "Imagine" after leaving the Beatles. John was the second US president. John was the sixth US president. John wrote Paradise Lost. John founded Calvinism. John wrote the Grapes of Wrath.


Surnames identify one in a global context more than first names do. The use by athletes is just another example of the same thing.

Why do Football players prefer to use their family name?
I was able to finish the first opus when I was young, but I have never been able to finish Impossible Mission II. 

Has anyone actually finished that game? Could they tell me what actually happens at the end of this game?
