They tend to take token "features" of cultural and ethnic dress as a way to prove what a truly international brotherhood they are. This is not exactly new - but its being featured on jw.org simply makes it more explicit.
This is hardly unique to the Witnesses. North American missionaries trawl the heathen peoples and nations for cultural legitimacy and "prove" it by showing their "catch" in emasculated ethnic wear.
"Hey, brothers and sisters back home in the good old USA: Look at my latest catch. I done got us some purty ethnic people who have got rid of their pagan trinkets and are now lapping up the Bible. Look at their toothy smiles, Praise Jehovah [or the Lord, depending on your religious proclivities].
What about those crazy "ten gallon" hats male Texan Witnesses' wear?
I bet they never show male Papua New Guinean Witnesses in their tribal loin cloths. No such luck.