They have never stopped being a thing on certain routes with little or no competition. The ULCCs price on a one way basis, so the majors follow for the most part but not when they don't need to. LAX-PHL is dominated by AA, the only alternative I see in September is a single NK redeye. So AA gets to set the terms instead of taking them.

DCA-LAS also has roundtrip pricing, for instance.