It seems to me unwise to hype the evidence that one is going to provide. Likely better to simply say that he is going to present good reasons that the suspicions of many Americans that the election was fraudulent is justified.
I don't like for people to give the enemy warning either, but thinking about this in a different way, it occurs to me that hyping it may get him a bigger audience for his reveal, and if it *IS* something significant, it gets much harder for the media liars and the politician liars to downplay it or dismiss it.
The bigger the splash, the bigger the potential impact of the evidence.
I think he's making it into an event to get the message out by going around the media-liars controlling the airwaves.