Though in one sense it is true that theories of cultural evolution lag behind their organic counterparts, in another respect cultural evolution is on the leading edge of evolution itself. If you look at most recent significant changes in the world, many of them involve cultural evolution. For example, memes - more than genes - are responsible for space travel, computers and the internet. Cultural evolution is on the cutting edge.
Cultural evolution is also on the leading edge of evolutionary theory. Organic evolution is a done deal - and has been for over a hundred years. There, researchers are mostly putting the icing on an existing cake. Cultural evolution is where the real action is. It is where new researchers can make an impact and make important discoveries.
Cultural evolution is of enormous social and political significance. A proper scientific understanding of how culture evolves is critical for making good policy decisions. Cultural evolution is much too important to be left to cultural anthropologists, who have failed to get to grips with the topic for over a hundred years and seem to suffer from poor scientific literacy.
Lastly, the role of cultural evolution looks set to become ever more important as time passes. In particular, memetic algorithms - which emulate cultural evolution - look set to play a critical role in the development of machine intelligence. Memetic algorithms and memetic programming are similar to genetic algorithms and genetic programming - only they are inspired by cultural evolution rather than organic evolution. Machines, like their human inventors before them, look set to harness the power of cultural coevolution - in order to attain the rapid rate of change which will fuel their future expansion and prosperity. The "code rush" as some call it. It is on.