I think this stems from the desire to be part of the group; to show that you belong. People want to identify their heritage, yet not have that isolate them in any way.
This is what i had always attributed it to. The 'patriotism' card is played pretty heavily in America, but so too is the effort to display diversity (to a palatable extent) and one's heritage.
And so people remain 'free' to identify themselves on the basis of where they are from, but only if they add the 'pride' of where they currently reside.
Meanwhile, few people where i currently live proclaim themselves only as 'Canadian'. Even those who were born here, inevitably feel inclined to refer to their parent's parent's homeland!
It is nice that people have confidence to add colour (pun not intended) to their origins, without having to dilute this sense of individuality to appease the flag wavers.
I am certainly liberal, but there are aspects of this political movement that are insane.
In Vancouver there is a thing called a Japadog
; A road side hotdog vending trolley, that has dogs with various bits of herb / spice / wasabi etc in it.
Some piece of liberal bullshit has brought up the question of whether 'jap' is too derogatory a term to prefix this vending outfit!
Important stuff! Far more vital than the tourists mixing with street meth smokers 10 blocks away!