Risk aversion "why are you quitting when you have a great job" is an individual personalty trait, not one of a whole unrelated group of people. You can find plenty of Americans who would say the same thing.
On top of that, you can't appreciate success that isn't there. You quit your job to start something, that's not succeeding so they weren't appreciating success. Odds are that you would fail miserably.
No, my bet is that what your seeing here is your friends are happy you're trying something you've probably been talking about doing for a while. They're probably your friends because they share some of these same interests, so in addition to seeing a friend do something they want they have the same drive to do it and understand why you would take that risk. Others around you that are not so close are making a risk assessment based on if they were in your shoes what would they think. If starting a business wasn't their interest, that's a huge risk to take for little/no reward. None of it has to do with Americans or Canadians.
Actually, you're a part of why Canada has a struggling tech sector. You moved to the US to start a business. Probably for the same reason doctors do, if you make money, you'll make a shitton more in the US. Other than money, there is no real reason to move to the US from Canada to start a business.