He did it because he thought it would be cool to free solo a building. He grew up idolizing Alain Robert, a french soloist who made his bread and butter out of soloing buildings. The guy was free soloing for free on his own without telling anyone about it for years, living out of his mom's minivan and eating cheap food, the media attention just allows him to be more comfortable as he keeps climbing obsessively. Also running his foundation probably gives a lot of meaning to what he's doing, he'd just be your average dirtbag loser otherwise.
I'm going to add that his coolest achievements were done with ropes. The friendly race to climbing a route graded 5.15 with Sonnie Trotter and Tommy Caldwell is a lot more interesting to me.