United proudly is the only major airline that has kept the ban on carry on bags for basic economy customers. In fact they’re more punitive than that, even. A basic economy customer who isn’t checking a bag isn’t allowed to check-in online or via app. They have to show up at the airport early in order to stand in line to check in, so an agent can personally verify they don’t have a carry on.
Airlines have rolled out basic economy fares between the US and Europe but the carry on bag restriction didn’t take hold for transatlantic travel. Now it seems like it might not be able to even if airlines tried.