Honestly? Because I am not French and I just wrote very thoughtlessly. Sorry, no further reasoning behind it.
[0] https://en.wikipedia.org/wiki/Les_Olympiades
[1] https://fr.wikipedia.org/wiki/Olympiades_(quartier_parisien)
Interestingly, both articles first words are "Les Olympiades", but:
* "Les" is in bold in the English one, as if it was part of the name, while only "Olympiades" is in bold in French
* The French article says "the Olympiades are" while the English one say "the Olympiades is".
Porte d'Italy on the other hand is clear, there's only one interpretation, and therefore the article is not part of the name.
I am not saying this is right, just my brain doing brain things. I apologize if correctness is important for you, I will try to be more precise going foward.