Why doesn't the U.S. use a 24-hr clock?

I've used the 24-hr clock for about 5 years now. My phone switched over when I visited Scotland, and I liked it so much that I never went back. I haven't had a single issue with getting alarms confused, however just this week my husband and sister have both accidentally confused AM and PM when it came to alarms.

Using a 24-hr clock format eliminates this issue and is far less confusing in the end.