I am asking this as an American. As I know "No taxation without representation" is commonly cited as a rallying cry for the American Revolution. But also the question applies more broadly. Why not grant Canadians/Australians/Indian subjects representation in Parliament? Considering these territories are independent now, it seems like there must have been pretty strong reasoning for why Britain would prefer to grant independence than representation.
Something to consider is that up until 1832 the UK didn't grant parliamentary representation to some of its largest cities and towns such as Manchester.