Tiens, apparemment Steam fait partie de ces logiciels qui atomisent tout quand on les désinstalle :

https://support.steampowered.com/kb_article.php?ref=9609-OBMP-2526
Warning:
The uninstallation process deletes the folder Steam was installed to to ensure it is fully uninstalled. If you accidentally installed Steam to a folder containing other data, for example C:\Program Files\ instead of C:\Program Files\Steam\, STOP! Do not run the uninstaller and instead carefully follow the instructions below for Manually Removing Steam, except only delete Steam-related files in step 3.

C'est vrai, pourquoi corriger un problème quand on peut changer la doc à la place ?