Siamese Origins

The Siamese cat is reported to have originated in Siam (Thailand). Old paintings show a cat with darker color on the ears, face, paws and tail. There were large classes of Siamese shown in the U.S. in the 1960s. The large Cat Fancier's Association show in Houston, TX, quite often had as many as 65 to 70 Siamese. This is not true in the 1980s in the U.S. Eight or ten Siamese are considered a large class; two or three is an average entry for most shows. What happened?