It's for entire website, not just tutorials, I guess it made sense to someone sometime or was picked randomly, the commit doesn't say.
I don't see a problem here really, it's not bad that tutorials are centralized and immutable IMO, if someone makes a translation, it can be sent to you for proof reading and hosting on site, no reason to allow people to grab stuff off the website and run with it.
Although a promise like the Qt/KDE one that all of the website code and documentation becomes much more permissive if you abandon or attempt to close it would be nice and reassuring that even if all of the team is gone SFML can continue and use old resources.