This news all comes courtesy of Nick and More on twitter.
According to them the Korra Book 2 Premiere got 2.6 million viewers. This is a pretty big step down from the Korra Book 1 premiere which got 4.5 million, add to this that most Book 1 episodes got around 3.5 million and you can see the issue.
I think there are a few reasons:
1/ New Timeslot - Korra changed from 11 in the morning to 7 at night. That is a big change. It may take a while for people to adjust and the ratings to go back up. Not to mention more competition at a prime tv slot.
2/ The massive wait between Book 1 and 2. The fandom will always be there to give the show some definite ratings, but much of that number is more casual fans who do not keep as up to date as us. Given the way Nick handled Korra in the aftermath of Book 1, it makes sense that many people who watched Book 1 had zero idea that the show was coming back.
These in my opinion are what led to the drop in ratings. I do think that the show will gain viewers as it goes on, word will get out to more and more people and the numbers will rise.
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Secondly, we have a new episode title and the order of the next few episodes.
[caption id="attachment_8051" align="aligncenter" width="522"] October episodes.[/caption]
K203 Civil Wars Part 1
K204 Civil Wars Part 2
K205 Peacekeepers
K206 The Sting
K207 Beginnings Part 1
K208 Beginnings Part 2
The new episode title being "The Sting" and confirmation that Beginnings are episodes 7 and 8. The Sting seems an odd title for the episode prior to the Wan focused episodes, I am really eager to see what it refers to. It also means no break in airing at least up to episode 8.