Fairly big difference between asking "Why don't they...?" and "Why don't they just...?". The 'just' tacked onto the end of the beginning of the question implies it should be totally obvious.
It is the desire for knowledge.
I loathe semantic games in arguments as much as anyone, but I too often see "ignorance" being given some kind of special place in science, where it doesn't belong.
There's a reason why NASA didn't just dedicate 8 years, $2.5 billion, and a tremendous amount of human effort to land a rover called "Ignorance" on another planet.
Curiosity: in this glorious age of Google, Wikipedia, Wolfram-Alpha, and so many other free and readily available resources, it doesn't start with the words, "Why don't they just..."
Same thing. You cannot do anything with just "lack of knowledge", whereas you can do lots with either "knowledge" (e.g process it and extract more knowledge, conclusions, dis/prove theories etc) or curiosity (e.g obtain knowledge).
Lack of knowledge is passive. Curiosity is active.