12:00 isn't AM or PM. It straddles them, and isn't wholly either one because of it. That's what this is about. Some people could argue that noon is 12AM. Others can argue that it's 12PM. Both views have merit, and despite that, we need to agree on one or the other, because times are often written down and everyone needs to know what time is meant when someone writes "12AM." Since consensus on this has never been achieved, we just decided on something that people COULD agree on: noon and midnight.
The question isn't valid for 11AM vs 11:01AM, because crossing into 11:01AM doesn't put you into the afternoon like 12:01PM does. It's only a valid question at the transition time between AM and PM or vice versa. So, it was decided a LONG time ago to just skip the problem and say "twelve noon" or "midnight" (or "twelve midnight".)
