Kelly experienced a lot of emotional turmoil after the release of Breakaway, and so My December ended up being a darker album that was not nearly as pop as her previous two records. RCA did not like that at all. They went as far as to offer her $10mil to exchange five songs off the album for more "radio-friendly" tracks, but she refused and insisted on the album being released as she wanted. There was some back and forth drama and long story short, RCA released it how she wanted however they refused to promote the album at all. The original arena tour for the album had to be cancelled and scaled back to a theater tour. They pulled radio support for the lead single just, like, 9(?) weeks after it was released. And they did not release any other singles from it in the US.
To give you a picture of how much RCA did not support her and this album, Clive Davis even went as far as to bash Kelly/the album at a big worldwide conference for RCA/Sony Music Entertainment. She found out about it via Randy Jackson.