Because, generally speaking, you don’t edit PHP code of your website through the PHP code of your website. Most people use either one of our web based file managers, of a code editor on their own computer.
Because I’m human and I can’t be around 24/7.
This message means that the code will only run on PHP version 5.3 and older. The oldest version of PHP we offer is 5.4.
PHP 5.3 is very old and unsafe. I don’t think there are many hosting providers available who still offer that version of PHP. Either the author of the software needs to update their code, or you need to use different software.
That looks like a corrupted WordPress installation. Did you update WordPress recently by any chance? Did the update complete successfully?