Why comments ignore?

Answer 1

Are you talking about the comments written in a source code?

The point of these comments is to help the reader understand the code better. You want these comments not to have any effect on your program.

Answer 2

When the program is compiling, the comments are knocked off at the first stage.
That is when the program is compiling, first of all all the spaces are removed and the compiler interprets the comments as one "space" character, so they are actually removed before the program is compiled.