Hi Fasho - and thanks for posting!
Bog and Countdown are not in the rotation at this time. The reasons they are not in rotation is that they are prone to heavy spawn camping/trolling and can become near insufferable with large amounts of players, and/or are simply unpopular by the majority and create a tendency for players to leave when they do come up.
Regardless, it is nice every once in a while to throw them in - even if it is not conducive to the preferences of most.
Whenever they do come up, it is because an admin (someone with {FH} tags) has manually changed it to that particular map.
Thanks for asking!
FH|McCheese