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of course Facebook isn't random....
Facebook is totally "engineered".... it's basically the biggest single advertising tool on the web (in the world?).
Think of it like this - Grocery's in the supermarket are not stacked randomly on the shelves - it's very cleverly arranged so that certain items are at eye level, and color co-ordinated etc etc.... designed to sell based on the information collected by every checkout in the store, in the country.... everything feed's a huge data base, that uses empirical model's to improve / control sales and marketing campaigns - they can sell these campaigns to the product manufacturer for large sums.
Facebook will employ similar models in exactly the way's you detailed in the OP - and of course, probably much more intricate data control techniques too. They own so much information about general populations and global trends it's scary.... and of course - highly highly valuable.... Facebook is a business at the end of the day - what does it sell? You and me....