Back in the day it was reasonably common for CMSs and forums to only have an index.php, and routing entirely by query string (in form-urlencoded form, people were not savages). So you would have index.php?p=home and index.php?p=shop. Or index.php?action=showthread&forum=42&thread=17976. It should be immediately obvious that in that scheme 404 is indeed the correct answer to unknown query parameters
In fact lots of sites still work like that, they just hide it behind a couple rewrite rules in apache/nginx for SEO reasons
In fact lots of sites still work like that, they just hide it behind a couple rewrite rules in apache/nginx for SEO reasons