Grady Eifert for Purdue [basketball] is a preferred walk-on. He ended up earning a scholarship I believe the last two years, partly because he truly did earn it and partly because Purdue had the room.
Remember that kids come from all sorts of different walks of life. Eifert's dad played for Purdue and his brother plays football for the Bengals, so if nothing else I'm sure his brother can afford to help him with tuition. Purdue's transfer from Dartmouth, Evan Boudreaux, comes from a wealthy family [his mom is CEO of Anthem healthcare], so although he is on scholarship, it's not like he couldn't have become a preferred walk-on if he wasn't as heavily recruited.
I don't know about any of the players in that article, but one of them mention the value of a UGA degree. It's possible, if they come from a family that can afford school, that the chance to get a UGA degree and MAYBE someday even play for the Bulldogs is worth the tuition.