That's news to my US vet friends. The most recent left the service two years ago, and they most certainly did drill. It's part of basic training, and it's used all the time in ordinary interactions. It's not taught for the reason it was taught in 1750, for sure, but it is absolutely taught.
Because it's a vehicle for introducing raw recruits into acting as a unit, following orders immediately and without hesitation, functioning cohesively with your foxhole buddies...it's a simple but very effective training technique on the path of creating soldiers out of civilians.
Similar rituals occur, for instance, in Japanese corporate culture, with mass fitness exercises and award ceremonies with organised standing, to enhance team feeling and corporate loyalty.
So when I see a whole unit marching completely out of step, in a formal unit parade? Followed by three out of four other units in the parade doing the same? That's no accident. We simply disagree, I'm afraid. Which is fine. :)