Why does it have to be in the standard library when adding it as a dependency involves adding just a single line? Since (a) there's no one true way to do input

Why does it have to be in the standard library when adding it as a dependency involves adding just a single line? Since (a) there's no one true way to do input parsing, and (b) most projects don't need to interactively ask for input, it doesn't sound like something that belongs in a standard library.