There are per-nation limits on the number of green card holders that can become citizens every year. Maybe they want to be citizens, but aren't allowed to be?
Meanwhile, a lawyer friend of mine had to advise a client of his not to go home to visit his dying father, because he might not be allowed back in. He's lived in the US for twenty years. He owns a business that employs six US citizens. He won't get to see his father again, and a father won't get to see his eldest son on his deathbed.
Do you have any idea what's involved in an immigrant from a Muslim country becoming a citizen? Without some sense of the requirements, you're assuming he doesn't want to be a citizen, when it's quite possible that he does, but hasn't been able to due to quotas.
Meanwhile, a lawyer friend of mine had to advise a client of his not to go home to visit his dying father, because he might not be allowed back in. He's lived in the US for twenty years. He owns a business that employs six US citizens. He won't get to see his father again, and a father won't get to see his eldest son on his deathbed.
So yeah, be smug. Enjoy that.