The purpose of the pre-announcement hype was to get people to tune in to their TVs to see who he'd pick. Trump was saying at least a week before the broadcast just when he would announce his pick, then telling people during the day yesterday to tune in. With the disinformation leaks pointing toward a number of different names being the "sure thing", he built suspense. Watching the announcement on TV would be like watching the final episode of some show like The Bachelor, or Survivor.
Kavanaugh's goal in his speech wasn't to reassure hard-core conservatives. It was to win over popular opinion of the nonpolitical population before the media had a chance to plant the view in people's minds that he was some sort of monster. The democrats and media are hoping to get the (generally) nonpolitical population fired up to put pressure on their Senators to oppose Kavanaugh's confirmation. The approach by Trump/Kavanaugh was designed to preemptively smother the flames.
“The approach ... was designed to preemptively smother the flames.”
It’s not complicated, I can’t figure out why so few seem to get that.