Learning the Route Structure of a Website
There is a good chance the website has its API available for you to use? Inside developer tools, look at the Network tab and look for AJAX requests or XMLHttpRequests as a hint; perhaps make use of a requests type-package and go from there.  
There is also a very good chance the website follows a Restful architecture to create its routes. Surely there are interesting reads on the very first results-page of Google for this topic; stack overflow answers most likely.
However, if you're question is why would a website not completely exposing its backend then you might not have considered the consequences.
I found a website i want to send POST requests to and then get the HTML code of the following GET request. Is there any way I can find out how these routes are organised? I wanted to do multiple searches by using a form on the site while looping through an array on a website through python.