I am taking over an existing PHP project. I noticed that the previous developer uses a one index.php page for the entire site, currently 10+ pages. This is the second project that I have seen done like this. I don't see the advantage with this approach. In fact it seems like it over complicates everything because now you can't just add a new page to the site and link to it. You also have to make sure you update the main index page with a if clause to check for that page type and then load the page. It seems if they are just trying to reuse a template it would be easier to just use includes for the header and footer and then create each new page with those files referenced.
Can someone explain why this approach would be used? Is this some form of an MVC pattern that I am not familiar with? PHP is a second language so I am not as familiar with best practices.
I have tried doing some searches in Google for "single index page with php" and things like that but I can not find any good articles explaining why this approach is being used. I really want to kick this old stuff to the curb and not continue down that path but I want to have some sound reasoning before making the suggestion.