It's no 'rig'. The site is run by server computers, and there is an algorithm that determines what subcategory a question lands in, when you click "Submit". Keywords in your question determine where it goes. Ever notice some users preface their question with "Politics" or "Polls" or "Religion"? That's to help ensure their question lands in the subcategory they desire, so they don't have to move it there BUT, since all users can move their own questions, it's easy enough to click "Edit", "Edit category" if your question lands in the wrong place when you Submit it.
After its initial landing on the site, question moving is 100% up to the OP (original poster) and any Level 7 user who chooses to relocate a question, for any reason (be it to move it to a more appropriate subcategory, or to abusively move it to an inappropriate subcategory to harass/abuse the site or OP or to increase chances it may be reported and removed).