If we look the period 1600-1700, bagpiping was hugely popular in England..as already pointed out, there's nothing Irish or Scottish about it. And plenty of pipes will have gone to America on ships in that period. The peculiar thing that McGrath is discussing is the fact that they didnt acclimatise and generate a distictive American style of piping, like Appalchian fiddle or cajun accordion. But you also have to consider that they also died out in England more or less completely, in the same period that they werent catching on in America. They just went out of fashion. Blasted out of existence by the rise of the Italian style fiddle, presumably.
    I dont think difficulty of manufacture in America can have any bearing on the question, anyone could have made bagpipes in America as easily as they could in Britain. And presumably did in the 1600's. There may not be any that have survived, but then how many sets of English bagpipes are still knocking about from that period?
This is a very interesting question of McGrath's, but I fear it will be as impossible to answer as "why do skirt lengths go up and down" or "why dont people read Bulwer Lytton any more?"