And also, still, fear of terrorist attacks. The 9/11 hijackers went to flying school, for example. So now the official policy seems to be to use any excuse to shamelessly collect as much information about as many visitors as possible, and to make the whole process a much greater obstacle by requiring a personal interview and charging money for the insult, from a hefty visa fee to nickel-and-dime fees for information. (Though I wonder if the last is actually a product of German law or business culture in some way, as there seem to be other large institutions such as the Bahn that also refuse to provide free telephone information, and that's really not customary here.)
I'm really sorry. I find all that rude, unethical, and distressingly Orwellian. And it's actually short-sighted policy as well, because it discourages people who might otherwise have come here, developed a more positive view of the US, and returned home more willing to consider our perspective and urge their politicians to do the same. So I apologize on behalf of my country.
But I hope that won't deter you from visiting anyway. It would also be sad to miss out on a chance for travel and cultural exchange just because of a pernicious bureaucracy that is still learning how to deal with the new threat of terrorism. Hopefully in a few more years (or decades) the pendulum will swing back in a more sensible direction.
At least, in the few cases I've known of at first hand, once you do finally get there for the interview, it's usually fairly short and businesslike, not as unfriendly as some of the preliminaries. I hope it will all go smoothly for you too. (-: