occam's razor would indicate this is a lot more likely than navigation by moon or any reproductive reason.
it just seems fundamental to all life, though. the sun is a prerequisite for life, after all. like, if most types of animals on earth were in a room filled with pure nitrogen and there was a hose in one corner trickling out oxygen, all the animals would end up over by the hose. granted, that's more out of necessity than needing light, but my point is that the animals would be about as conscious as to why they were going toward the hose as they are about going toward light--it's just what you do, y'know?