The more I think about it, the more I think the reason lies somewhere else. As long as the company itself stays US only they shouldn't have to worry too much about other nation's laws (unlike Amazon, who have local subsidiaries everywhere). However, they would potentially be sending large sums of money to places outside the US. Which means they might end up funding the wrong kind of people. Oh hay, have you heard about my suicide squad Kickstarter?
Or god forbid, some evil terrorist organization like *cough* wikileaks. Now that Uncle Sam wouldn't like at all.