Hi Jen thanks for posting in the community - I'm happy to help! Unfortunately automatic generation of a sitemap diagram based on your website's URL isn't currently supported in Lucidchart. Our templates remain the best option here!
However we're always looking for ways to improve Lucidchart and your feedback is the best way for us to do that. Would you mind adding your idea to our feature request form? Ideas submitted to this form are passed on to the product development team for their consideration.
As a growing company we take our feature requests very seriously. We are continuously looking for how we can make our product more useful and effective for our users and we pass that information directly to our product development team.
Thanks for your request and I apologize for any inconvenience this causes you.