Well let's keep in mind that the Kong rumor was about people being secreetly pulled in, rather than opening the backdoor and soft opening due to the entrance being not ready yet/blocked like Soarin was. (which I admittedly forgot about until just now)
When it comes to those "secret" softs, WDI and ops want to keep those on the down-low. In contrast, a "formal" soft opening is already designed to pull people on the attraction. The entrance is built to do that. So obviously people in a theme park will gravitate towards that.
I think Disney has changed the way they can do softs and had to altogether drop the more secretive "play test" softs due to the burgeoning rise of communication. Think about the throngs of crowds waiting outside Diagon everyday. This is due to social media, people wanting to be first on the scene and showcase that as soon as possible. It's just another thing lost due to the rise of communication, just like how Mr. Toad and Light Magic changed Disney's perception on how they can't control the message as easily. Nowadays it's blown up so huge that literally anybody can access this information, not just super fans. Just a comment on change, that's all.