You don't understand the reason? Me neither.
Another case. A friend of mine, again, it's somebody I know in person, who graduated from a med school in Texas, and obtained RN license in US. Later on she moved to Ontario. Ops, she got to go back to college to take a couple of credits, then go thru the exam to get her Ontario license in order to practise. I am sorry I have to surprise you again.
Yes, I know that Canadian licensed RN is welcome to USA. However, the other way around is tough. You cannot drive through it. Good night and good luck.