You realize it's the year 2018, yes? Why on earth would any company today, let alone one like Disney, blow their budgets on a bloated TV special with D-list celebrities and bad musical numbers when they can more effectively reach people online with more focused, targeted content??? Instead of people being relatively clueless about a Disney project until it's open, Disney (and all the park geeks like us) are keeping others informed throughout it's development and construction cycle, providing all sorts of content (video, photos, blog updates, live streams, press days) along the way via official sources and social media. Plus once soft/press openings take place, the internet is literally flooded with all sorts of great third party content as well. Doing that in the form of a TV extravaganza just makes no sense at all. (They do still save that stuff for big anniversaries though, like Disneyland's 60th).
I say this a lot around here, so not to beat a dead horse, but people really seem to just disregard how much media consumption has changed since the park opened in 1955.