First off, just a bit of a nitpick, but as I understand it the Evangelical/pentecostal side of Christianity is doing pretty well, or at least it's not suffering from its members literally dying off (far from it, in fact). That was also my experience from about five to ten years ago.
Second, I'd argue it's way to early to conclude that abandoning religious moral guidance is a success. At most it's an (unprecedented?) experiment that so far seems to work.
Western European morals and philosophy are no longer influenced or controlled by religious considerations. I wish I could say the same for Australia.
While Western Europe is far from perfect, it's also not a morality-free wasteland of depravation and selfishness. This is what happens if you abandon religious moral guidance: nothing.