It's
Banned
Why would the Brits give independence to a place that will soon have a larger population than them as a single nation? They will want to divide and rule. If there is an overarching loose structure they will stay within it..
Because they want their loyal colonies to be stronger. They will be stronger if they are united. Good for the colonies= good for empire= good for Britain. Inside an empire, it's not a zero-sum game. You might notice that Australia and Canada are federations too (not yet as populace, but...).
Divide and rule, divide and rule, divide and rule, divide and rule... The evil Bruddush bringing tension and misery where there was just harmonious utopia before. Yes, that's right, instability within an empire is really good for business!