I'm not getting testy, don't worry. It just surprised me that you thought it wasn't that difficult. Made me wonder whether you had ever folded it.
It's a closed sink that is really hard to maneuver. You have to deal with a lot of layers, sink in at a large angle--that sink is 67.5˚ wide. It's completely unnatural. And, to make matters worse, this is a truly closed sink. Oftentimes you can partially unfold to perform a nice neat closed sink. As I remember, this was not possible. And since all that's hold that assembly there is a simple valley fold through many layers, a third hand would come in really handy.
Open unsinks are far more difficult to do than closed ones. Closed unsinks are fun! And if you have large paper, they're not hard at all. Heck, that Fujimoto hydrangea is entirely made up of closed unsinks! Closed unsinks and closed sinks are some of my favorite standard moves. I use them whenever possible
The Dancing Crane closed sink, Brian Chan's Crab's closed sink (but with large paper it might be doable), some weird assembly in Marc Kirschenbaum's 1-piece chessboard--those are the most difficult folds that come to mind. I know there have been others.