The peoblem with building these kinds of detectors is that we don't know what dark matter is--or even whether it's made of particles at all. Without knowing what it's made of how do you know what to look for? There is a countless number of theories that claim to explain dark matter and so far none of them have worked. What are the chances that one of them is correct--the one that you happen to be testing? It's just a way for them to get paid.