I said it before and I'll say it again: Nickelodeon made a mistake rushing its release of Book Three without an adequate marketing campaign. They gave us three episodes on a single day and they will now skip a week to give us another two. Don't come complaining to me about ratings if you didn't promote your product and can't even keep your schedule together.
So do they want to cancel the show due to low ratings and are just being coy about it?
The reason why Season 3 was abruptly premiered and slotted on a Friday in June was due to... Mexico.
Nickalodeon originally intended to reveal Season 3 at the San Diego's Comic-Con this year, then market the season, and premiere it in the fall during primetime. However, Nickelodeon's affiliate in Mexico, MundoNick, leaked four mid-season episodes while working to subtitle and dub them in Spanish. Nickalodeon, in an attempt to regain control of the situation, decided to immediately premiere the season in America. That is why this season premiered during a bad time slot without any marketing.
Link: Forbes: 'The Legend of Korra' Should Not Be Premiering on Nickelodeon This Friday
... and now the show's ratings are taking a serious hit, and there is a rumor of Korra getting canceled after Season 4 due to low ratings.