I paused when I read the weird "checking political orientation before taking video maker seriously" aside - as if any take on D&D has to automatically be filtered through cultural or political ideology. But, moving on...
My purely speculative take: D&D was already on a bit of a(n inevitable) downturn after the crazy peak of 2021-23ish. That, coupled with the distinct possibility that the new younger base just doesn't care as much about new editions or books (see below), and for older players the OGL kerfuffle and ongoing stories about corporate BS was a turn-off. Plus there are so many other options now. I think also the fact that it wasn't actually a new edition made the event less exciting. So it didn't quite grab the newbies as "must have" and old-timers have been there, done that with new editions, and this wasn't even a new edition.
Now I'm not saying it is like the 1991 X-Men #1, which was the largest print run in comics history and while it was a few more years before the market crashed, it represented a high peak after which everything went down hill (as far as sales are concerned). But I wouldn't be surprised if they printed a lot more than they sold, and that sales are at least somewhat disappointing to the bigwigs at Hasbro.
The "see below" anecdote: I work with teenagers, quite a few of whom play D&D. The ones I spoke with didn't know about the new books and didn't seem anxious to go out and buy them when I told them about it. My takeaway is that a lot of the "new D&D boomers" who started up over the last decade are pretty casual and approach the game quite differently than 35-60ish year olds who have been playing for decades. They just like to play D&D and most don't care about other stuff. For them, it is one activity among many, so the days of new waves of RPG diehards might be over. Not saying that no new players will become diehards, but it might be a generational difference. Under 25s live in a very complex tech, media, and entertainment environment. Older folks do too, but the older you get, the more time you had in the good old boring days of "There's nothing on TV, nothing to do, so I might as well do something imaginative/creative."
Meaning, the percentage of new players that form a deep bond with D&D is probably a lot smaller than it is with at least those of us who stuck around over the past several decades. I mean, lots of people peeled off from D&D after the 80s boom, so I'm not sure why now won't be different. It is the way of things. The best WotC can hope for, in my opinion, is to create a vibrant core game that keeps the "birds in hand" as much as possible, and is easy enough to get into to keep a influx of new players. But turning the supposed 50 million players of a few years ago into a new base was a pipe-dream.