They have 10 million users, so it's fair price to pay I guess https://www.wunderlist.com/world-productivity-report/
So, yeah, I guess it's not that outrageous, even if it is "just" a todo list app (it's a pretty nice one, though; I use it and mostly really like it).
10 Million active users? Or like me, installed it, abandoned it; like most todo apps.