...Because it's not. Let me clarify!

You do not NEED one of the topics from the explore page to get Boosted. Rather, if a Boosted story includes a healthy range of topics (including relevant explore page topics) then it can support that story performing better IF it is Boosted.

The topics on a story are NOT a factor in the story being selected for Boost -- but useful topics are a best practice to help a story can perform better IF it is Boosted.

Please let me know if you have additional questions. I really want to make sure that this misunderstanding doesn't get spread around.