AOG - // No one has yet answered the question why???? //
I have - at 18:15 yesterday - it is courtesy to observe a dress code when to fail to do so would be impolite to the host.
// Would the Queen and the Duke Dress in such a manner if they had paid a visit to Pakistan? //
Unlikely, they are a different generation, and the last time the Queen and Duke visited, there was less emphasis on cultural interaction than there is now.
// Why can't our modern Royals behave like British Royals? //
I think they are - they are the next generation of the Royal Family, and they are adapting to changes in the world in which they live, which is appropriate in my view.
//How far is this respective behavior by them to go, dressing up in the traditional dress of every foreign country they visit? //
Probably not - as I have already pointed out, the Duchess chose to respect the cultural requests of her hosts in terms of appropriate attire, and Prince William decided to dress traditionally, probably as a compliment to his hosts as well.