I can't remember a movie which had exploration as its theme. Is it hard to write a film about exploration?
Yes it is. "Exploration" is not really a theme. "Revenge" is a theme, "love" is a theme, "finding yourself" is a theme. Usually what we call a theme in fiction has something to do with characters, not with plot.
Exploration can be used as a plot element, a backdrop for some other, more tightly focused theme. But even then, it's a lousy plot element, because exploration never ends. You just move from place to place and see things that no one has ever seen, and when you've seen them, you move to other places that no one has ever seen and so on. There's no dramatic tension to be found there.