If you took your family from Canada to the USA, and built a life, then you decided to run for politics, and watch from the outside as Canada degenerated more and more.
You would use some of your influence to try get the USA to help Canada.
This is the 'right thing' to do in many aspects, however, this divides your loyalty. It is a betrayel to the American people.
The American people elected you to represent THEM, not to try nudge the USA towards helping Canada.
You have a conflict of interest. You cannot truely serve the American people because of this, you are always trying to nudge 'helpful' things to Canada with your roots. You are at odds with what they (And specifically MAGA) wants.
The same principle applies to Isreal. You cannot have dual citizenship in any aspect of government due to your ties to your old home.
Yes there are broad holes in this, but the core concept remains. You will never fully be invested in your current host country because of those ties, thus you should never be in a position to dictate that countries policy. You are biased and unfit to serve at higher levels.