Thanks for checking it out! I really appreciate the feedback.
The limited format of a pamphlet kind of restricts how much I could delve into the story but you touch on the main reason as described in the adventure in your third point. The Chief Scientist in charge of charting the asteroid's course is incompetent and simply miscalculated the trajectory. The reason for her miscalculation is detailed in the adventure itself.
The reason behind why the asteroid is heading towards a collision with the planet isn't really the main driving force of the story for Verden Prime but rather just a factor to keep in mind. The main tension arrives from the [SPOILER] twist that the asteroid is inhabited and that there is a sort of cult trying to preserve it. Do you fight them or do you try to reason with them? That is the main story.