Two simple reasons. First, "hello world" requires less explanation

  print "hello world"
  vs
  print ("hello world")

Second, printing a line to stdout is an extremely common and special activity (especially during debugging). There is almost no programmer-defined function you could write that has a function as fundamental as that of "print".

Larry Wall of Perl thought about these things in terms of Huffman Coding, i.e. the most common thing you might want to write should have the syntax elide any easily understood context.

In the case of "print", we know we're not talking about any random function here: it's the function for getting output to the terminal, one of the most fundamental operations in all of programming. So I think it's totally fine for it to have a special representation in the language.