Most "Index of" pages aren't meant to be public. They usually occur because:

By using the intitle command, Google looks for pages where the browser tab literally says "Index of," which is the default header for Apache and Nginx server directories. The Risks: Why You Should Be Careful

Here is a deep dive into what these indexes are, how they work, and the risks involved in exploring them. What is an "Index of" Page?

An admin forgot to disable "Directory Browsing" in the server settings.

When you search for , you are specifically looking for servers that are publicly exposing video directories. How People Find These Directories