Although there may be some, such as the same techniques being used to de-extinct other more recent species, I think a certain amount of it is "because it's there", and that the irrational desire to accomplish such an outlandish thing may provide motivation and funding from corners that otherwise wouldn't do so.
I think it was Jack Horner who was trying to reverse engineer a chicken back into a velociraptor and said something to the effect of that he didn't feel that his efforts would do anything to help humanity, but that the science justified itself, because it was what he wanted to do, to see if it was possible.
Of course, with that story, we have a great series of movies to tell us how it probably ends...