The American culture values individualism...and also has a strong "you can't tell me what to do!" reaction to social pressure. If those points are connected, I can easily see too much individualism interfering with cooperation even if the base ideas are not in conflict.

Evidence: who are the heroes in american TV and movies? The rebel against authority, the one that breaks the rules. Lethal Weapon, Die Hard, House, I could go on and on. We celebrate the idea of something we actively argue against in daily life.

There's also some weird connection between extremes of claiming to value individualism and idolizing authoritarianism that I won't claim to understand, so I could be completely wrong on all of this. I'm not positive that extremes of individualism are a death knell for cooperation...but I don't find the idea unlikely either.