That chip is pretty expensive. At $6.46/ea (in production quantities) it's a lot more than most cheap microcontrollers. For the hobby (/etsy/small-run-on-ebay)

That chip is pretty expensive. At $6.46/ea (in production quantities) it's a lot more than most cheap microcontrollers. For the hobby (/etsy/small-run-on-ebay) market there's also the fact that the average hobbyist doesn't have access to soldering equipment that is good at BGA parts.