Why a particular URL web address exists but its parent folder does not exist

For example, when I run the following command in linux:

curl -I https://assets.thalia.media/images-adb/68/a5/68a5b9c3-2c0a-482b-9965-98d2167b14dd.pdf

The server returns HTTP/2 200, meaning the file exists. But if I visit any of this file's parent folder, for example:

curl -I https://assets.thalia.media/images-adb/68/a5/

The server returns HTTP/2 404, meaning the folder is not found. It even does not show 403 (access forbidden). My question is why a file can exist but its parent folder does not exist?