Lots of people do though. Daniel Dennett (probably the most influential philosopher of mind in the late 20th century) for example had an evolutionary view of consciousness arguing it was favored by natural selection. And (if I remember correctly) Steven Pinker argued that consciousness was an epiphenomenon.

However there were pretty strong arguments against this idea as early as the 1990s, by Stephen Jay Gould and Richard Lewontin. Gould actually wrote an excellent paper against Dennetts idea[1].

I think Dennetts ideas were extremely popular but have largely fallen out of fashion. Basically what has changed is philosophers no longer take the human mind to be much more special then the minds of other species. What plagued Dennetts ideas the most was this notion of Darwinian fundamentalism sort of the idea that evolution was destined result in high beings like us humans. Modern philosophers (at least the good ones) reject this.

1: http://cogweb.ucla.edu/Debate/Gould-frame.html