It's because programs want a safe bet. If somebody went to med school in the US, you know the exact standards that they had to meet in order to graduate, so the risk of a dud is lower. If they went to med school overseas, you might have a chance of getting a brilliant superstar who just couldn't find a spot due to IMG status, but you also risk getting a person who is unable to communicate well with patients, make holistic clinical decisions, or effectively function in a complex healthcare system. Even if 90% of applicants are good doctors, you don't want to risk having one bad doctor out of every 10 people you accept.
That said, with scores of 240/240 (which are above average, but not super-impressive), you should be able to match into neuro programs if everything else is good enough. If your friend applied broadly and didn't get any interviews, I'd imagine that his personal statement and/or his rec letters were not suggestive of strong communication skills, a commitment to the specialty, and/or appropriate clinical demeanor.
I went to med school in Australia, I have several relatives who went to med school in Pakistan, and I'm currently training at a residency program attached to a "top 5" med school in the US, where I work very closely with the MS3/4 students. I also did some rotations at an "average" school in the US. Based on that experience and knowledge, I can say with fair certainty that the med school training here is most certainly NOT superior to the better schools in other countries, but it most certainly IS superior to the average school in other countries.