Of course they'd never want to promote bad projects in such a public-facing way. Meanwhile at DCA's Blue Sky Cellar...
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Pixar Pier is a bad concept, executed poorly, at incredible expense for what it is, yet it's still being highlighted nearly a year after it opened. In the meantime, there's a new billion-dollar land across the Esplanade that's set to open in a couple months that has remarkably little information available in the parks, but is largely blocked from view of average guests.
DCA's preview center opened in 2008 because they knew all the upcoming construction would be too significant to ignore. So instead of pretending like it didn't exist, they leaned into it and created an opportunity to get people excited for the park's future. Given that Epcot's core will also require several years of extensive construction, it makes sense that they want a similar location for guests to learn more, so all those poor CMs don't have to keep answering questions about what's behind the wall.
It's not about quality, it's about marketing. I suspect marketing is also the reason why they were willing to tear down perfectly usable buildings for this plan: it's a lot easier to get people excited (whether potential visitors planning vacations, or corporate boardrooms buying into expensive projects) if the change is more drastic. New must be better, right?