URL comes from Uniform Resource Locator. This means that it is the way to locate any resource used on your website. A page like an image or a script (css, js, …).
An analysis of a crawl reviews all the resources of your site … so the total number of URLs can greatly exceed the number of pages proposed.
To have a complete analysis, we must analyze EVERYTHING.
The proposed subscription formula includes a limit in URLs of all the resources to analyze and not only the web pages.