The SILL About page translated explains the list :

https://code.gouv.fr/sill/readme

Why this catalog?

The socle interministériel de logiciels libres (SILL) is the reference catalog of open-source software recommended by the French government for use throughout the administration.

This catalog helps administrations find their way around the open-source software they are encouraged to use, in line with Article 16 of the French Law for a Digital Republic

« They » is « a full-stack developer whose work has largely focused on working with web technologies ». You show you dislike lone developers building their own apps.