Why is everyone so crazy about this?
It's not even american news and it's a child birth.
1) American Media and culture happens to be quite fascinated by the British Monarchy, for some reason. Although, in fairness, it probably just fits in to the celebrity culture that America basically created.
2) This child will likely one day be the King of one of the most powerful countries and it's entire Commonwealth, which happens to be a World leader, and has one of the oldest and most important histories on the planet having influenced almost every single other country ever at one point or another.
3) It's not uncommon for celebrity births to be big news.
Besides, it's the birth of a healthy baby boy.
There's no reason to be annoyed or angered at such a thing.