(Full disclosure: family member works for Big Pharma)
You might not get them to admit it out loud, but Big Pharma sees the USA as the cash cow that funds R&D for everyone on the planet. If a potential product can't or won't ever make it to market in the USA, or if there aren't enough potential patients in the USA to be prescribed said product, then it might never get off the drawing board.
It's (unfortunately) that simple.