because separating time in to two chunks of AM and PM is useless when it doesn't condense the number down into less digits
like, I'd use it if there were three chunks (say, 00:00 to 07:59, 08:00 to 15:59, 16:00 to 23:59) so that the third digit never appears but as two separate 12 (two characters) hour blocks it's pointless