Because the text in the file is not a newline character. It's a backslash plus the character "n".

When you use Data::Dumper to print out a variable, it tries to escape all characters that need escaping to make it a valid string usable in Perl source code. As a Backslash would be used in a string as escape character, it needs escaping (double backslash), in order to produce a string that represents the original text (e.g. a backslash and the character "n").

You can check this with a hex editor (or "hexdump -C" on Linux) on the original text file.