I have a slightly different theory about the stalled progress on various attractions. The pandemic plays a part, but not because it significantly prevented work from getting done. Rather, Disney may be wanting to open new attractions at times when they both need and can accommodate an increase in attendance from them. If you open a new attraction at a time when you're maxing out at 35% capacity, you've effectively put a cap on how much draw you can bring in. Of course, at this point we can expect the capacity to be either raised or removed entirely by October, but they couldn't have counted on that at the time they announced the anniversary plans we currently know about.
What they also announced at that time was that the entire anniversary celebration will be 18 months long. My guess is that they'll continue completing and opening the upcoming attractions and other stuff over the course of the entire 18 months. Tron, Guardians, Play Pavilion, Journey of Water. Various other pending projects, like Space 220 and the Star Wars resort. Rolling these things out gradually rather than preparing a bunch of them to all be ready by October 1 might disappoint day-one anniversary visitors, but it holds a few advantages for Disney, and it serves 2022-23 anniversary visitors just fine.
Since day-one anniversary visitors are likely to be the hardest-core Disney parks fans, it's fair to feel a bit frustrated about that or even betrayed. It would be nice if the anniversary felt more like a show of appreciation for the fans who help make Disney the phenomenon it is. But from a business standpoint, there's no advantage to loading all the launches up for a date — October 1, 2021 — that will probably see four completely full parks and no available hotel rooms no matter what attractions are open. It makes more sense to launch something new when the spike from the previous big event is expected to start declining. And they know a good chunk of those day-one anniversary visitors will be back for some of those later launches.