Specific features evolve because at some time and probably for an extended time a bottleneck or "survival of the fittist" senario favored that feature. Once that feature is dominant in the genes of the survivors, that specific feature isn't going to instantly disappear just because the situation changed for the better.
Yep. I'm amazed by "science journalists" that explain evolution in Lamarck's terms -- environment forces change, rather than change fits the environment.