Probably because they want to start construction in conjunction with Avatar.
One widely held theory is that Avatar land will utilize not only Hollywood Blvd. and the Hollywood Backlot areas, but will also utilize land currently serving as the bus drop off. (A new bus drop off is included in the Eastern Gateway plans with a walkway through the former Carousel Inn lot, which Disney purchased, and a bridge across S. Harbor Blvd.)
If that is the plan, they would need the new bus drop off (and parking garage it is co-located with) built before demo-ing and beginning construction on the current bus drop off area. Given that the Easter Gateway project itself could take two years to complete, it means that Avatar couldn't start construction, essentially, for a minimum of two years. If Avatar is a 3-4 year build, it pushes this project completion to around 2030. This is not shocking to me but given Avatar was teased prior and officially announced in 2024, that's quite a while.
And...in the less likely scenario they build Avatar on the Simba lot next to Pixar Place Hotel, a similar dependency holds true: that parking capacity needs to be replaced elsewhere (with the Eastern Gateway) before construction on Avatar begins.
All this is to say, it *seems* that the Eastern Gateway -- a project Disney has been wanting to do for years -- is the linchpin for Avatar either way. And while it's a substantial project (a 7,000 space garage, bus drop off, walkways, bridges security checkpoint...) it is not "themed," "ride engineering," or "entertainment design," so to speak, and could be tackled in a routine way by consulting architects, engineers, and contractors.
I'm just surprised there's been no permit activity yet, but when something does get filed it will really kick off the Avatar timeline!