Because people are dumb?
More seriously, I suspect a lot of people wouldn't expect themselves to have anything to contribute to fields outside their area of expertise just as they suspect outsiders wouldn't have the ability to make breakthroughs in the area they are "experts" in. This seems like the kind of activity that yields no results at all until you find something important, so maybe it seems like a waste of time?
Sometimes, scientific discovery is just a matter of sitting down and using the tools of "connected science" already available to us. Stories like this one underscore the need for generalists:
From Reinventing Discovery by Michael Nielsen (a past Singularity Summit speaker).