Don't know where the idea got started that robes are somehow integral to the Mandarin's character. In the comics, he only wore robes for a couple of appearances in the nineties.
Originally, he wore kung fu pajamas, almost a ninja outfit from the neck down, but with a supervillainy headpiece.
In the seventies and eighties he wore a barbariany looking outfit.
In the 2000's he's been mostly in a business suit
There is nothing vital or historically important about putting him in robes.