Why only six episodes?

Before even posting a topic asking a stupid question, suggest you google it.
Even though NOW all 12 episodes are out, you can find your answers on wikipedia.

If you go to the list of mock the week episodes, you can see from series 9 onwards, first 6 episodes airs in June and July, then episodes 7-12 airs Sep and Oct.

If you can see the pattern, which is not that hard, then you would've had your answer already on Aug 30 instead of posting it here waiting for someone like me telling you where to find the answers.

Google and wikipedia are your friends. Use it next time then if you cannot find the answers you want, then you can post it.