The XML-RPC WordPress specification was developed to standardize communication between different systems, meaning that applications outside WordPress (such as other blogging platforms and desktop clients) could interact with WordPress.
This specification has been a part of WordPress since its inception and did a very useful job. Without it, WordPress would have been in its own silo, separated from the rest of the internet.
However, xmlrpc.php has its downsides. It can introduce vulnerabilities to your WordPress site and has now been superseded by the WordPress REST API, which does
