"Because the script called for it.
Hollywood had a long tradition of casting actors/actresses in roles that were different than their cultural background. This was really no different. Usually it was caucasians playing a character from another ethnic group. Westerns were often quite guilty of this. And how about John Wayne playing Genghis Khan in the Conqueror?Actually, look at the entire cast of that movie. There are tons of other examples.
What they could (and maybe should) have done is change Khan's character to hispanic.
Looks like in the initial scripts Khan was supposed to be Scandinavian or an "Aryan" Sikh (whatever that is
). I think it would have been so inappropriate to have a race of "supermen" be led by an Aryan. I'm glad they changed it to be someone of different ethnicity (even if he wasn't really).
I think their intentions were good when they intended to portray Montalban as a Sikh. But even as a child when I saw Space Seed for the first time I never though Khan was an ethnic Sikh (or Indian). I thought he was just doing a Lawrence of Arabia getting his tan and mannerisms after living with them for years. Perhaps McGivers though Khan to be a Sikh because of his "20th century Sikh supermen" hair-do and clothes that she'd seen on historical documentaries of the time,.