It used to be thought that ~95% of the genome was "junk DNA", i.e. DNA that was there either for evolutionarily historical reasons, or as the remnants of viruse

It used to be thought that ~95% of the genome was "junk DNA", i.e. DNA that was there either for evolutionarily historical reasons, or as the remnants of viruses or other mobile bits of DNA, but which no longer performed a significant function. The principal finding reported by ENCODE is that the proportion of the genome which has no ascribed role has now dropped to 20%, 5% codes for "traditional" genes and 75% is this new stuff. A lot of that new stuff appears to be regulating the activity of the traditional 5%. As to the motivations of the scientists involved, they will be a mixture of pure intellectual curiosity and the quest for cures to diseases. Of course they also would like to be paid, and must therefore dress some of their motivations in language likely to motivate their ultimate paymasters, i.e. the public.