Most junk mail is targeted by zip code. Some stuff happens because you have a “relationship” with the company (usually a credit card, or at least a loyalty card), but for the most part you and all your neighbors get all the same junk. We have a trash can near the mailbox, junk mail only travels 2 feet.
I didn’t know how it originated. I wish the environmentalists would shut it down (because it kills trees needlessly); it just fills garbage cans. I understand the postal service is opposed to getting rid of it, as it would probably kill half their business.