...that Siamese cats just aren't like other cats?
It's probably because they aren't. For a long time we believed that Felis domesticus is the domesticated form of Felis sylvestris, the European wild cat, and was first domesticated on Cyprus...and that the cat then spread through the world.
Because, completely independently, in China, Prioinalurus Bengalensis was domesticated. That's the Asian leopard cat, still used to create the Bengal Cat breed.
So, Asian cats seem different...because they are different.