Delta is considering dissolving its “low cost carrier-within-a-carrier” called Song.
The wisdom of these operations has always been questionable at best.
Delta used to offer a similar product to and around Florida. They resurrected the idea with Song, and expanded it to cross-country flights.
USAirways used to have Metrojet.
United had “Shuttle by United” on the West Coast. There’s still the occasional 737 in Shuttle by United colors (with less legroom and no ability to serve hot food) disappointing frequent travelers when they’re surprised at the gate. There’s the familiar joke about United’s current attempt, Ted, that it represents “the end of UniTED.”
Continental had Continental Lite.
It’s very hard to market two distinct products under the same brand. It’s hard to offer operational independence. And with different pay scales and work rules (the real appeal to the carriers themselves), they breed resentment within the workforce.
Southwest has a simple business model and it sticks to it. JetBlue, though with some trouble on the horizon, has been successful with its own simple business model.
Major carriers have a hard enough time figuring out how to make a single model work. Two at the same time has proven impossible, time and again.