The process of evolution is a natural sifting process which tends to preferentially reproduce individuals which are better adapted to their changing environments and tends to eliminate individuals which are less well adapted. After many generations, the better adapted individuals have become more numerous within the species which benefits the survival of the species as a whole.
I don't think the evolutionary process is necessarily "progressive". It simply results in organisms being better suited to their changing environments. Although species tend to become more complex with time, this is not the same thing (in my opinion) as being "progressive".
And when the environment is made less hostile, what would you expect?