It's really not surprising considering Nick's actions in the past with scheduling and promotion. They've removed or moved episode last minute without promotion, their scheduling is constantly different, and they've removed repeats from Nick, placing them on Nicktoons. They clearly don't care about the series or to allow it to do as well as it could. Just like the last group of episodes that were scheduled; the ratings were increasing and they cancelled the last premieres that were scheduled.
There's been a rumor that a executive at Nick doesn't like the show. Whether or not that is true and is the result of Nick's behavior in regards to the series is debatable, though there's no doubt the show isn't receiving the treatment it should.
It's possible that business relations and/or legal rights are at the heart of this issue. I've certainly seen fewer promotions compared to non-Spongebob shows, via Youtube. I always see every other show promoted in ads.