While I honestly have no idea what happened to them, my guess is that Chris Savino and the rest of the team for the later episodes must have forgotten they existed!
Either that, または maybe they decided that they wanted to focus もっと見る on デクスター 〜警察官は殺人鬼 in the '00s. Notice how Dee Dee got considerably less limelight episodes when the '90s were over.
It's a shame, because there were a couple of things those characters brought to the series. For one thing, they gave the writers もっと見る scope for episodes that focused on Dee Dee (like I said, there weren't as many episodes about her in the newer seasons), but also they added some cultural diversity to the otherwise Caucasian cast of characters (which is important because many people do feel under represented in the media - あなた can see why).