Regina said:
The answer is incorrect. Quite a lot of provinces have immigration programs when you can sponsor your close relatives (!!). And look at the United States, they allow to sponsor adult children as well as siblings.
So , in "federal Canada" it is not about adult children "who have to make their own decisions". Then what is it about really? I am still guessing.
The US does allow sibling sponsorship. However the wait times for sponsoring siblings are considerable. For countries with faster processing times, it's somewhere between the 10 to 12 year mark. For countries with slower processing times, I believe it's somewhere between 15 and 17 years (maybe as high as 20).
I think the answer to your question is that each country sets its own rules for immigration which try to strike a balance between family sponsorship and skilled worker immigration - and there isn't necessarily a definitive reason why one allows something and another doesn't. Each country has rules that are good and rules that are bad for those wishing to immigrate or sponsor their loved ones. And these rules have been slowly developed over years.
As you mentioned, the US allowed citizens to sponsor their siblings at the federal level - Canada doesn't.
On the other hand, in Canada, you can sponsor your spouse with no income. In the US, there's a minimum income you must be making to sponsor a spouse. So if you're out of work, forget about sponsoring your spouse - unless you can find a co-signer who's willing to sign a legally binding support agreement.
The US also classifies dependent children much differently than Canada. Let's say you want to sponsor your parents and your 7 year old brother. In Canada, you can include them in one application and sponsor them together. In the US, you can only sponsor your parents. Your 7 year old brother has to be left behind. Sure - he can be sponsored by you separately - but that will take somewhere between 10 and 17 years. Alternatively, your 7 year old brother can be sponsored by your parent. But not until they become citizens of the US. So either way, he's getting left behind for years.
Canada's rules aren't perfect. But the grass isn't always greener on the other side.