At the very least, there's much less hype than there typically is at this point in development. At this time in Shadowlands, people were getting hyped about Torghast and the crazy power levels you could take your class towards... granted that all got gutted, but that leads towards what's likely going on:
People are burned out with Blizz's promises and "Don't worry, this time will be different!" We always get some signs of change every expansion that point towards a great experience, but Blizz is their own worst enemy when it comes to following through. If one reads between the lines and pays attention to what Blizz says and does (helps if you're part of the testing process, too), the situation where Blizz is now is not really a surprise.
My prediction is that there will be a spike in players at the start of the expansion as usual, but it will be very muted compared to normal. I wouldn't be shocked if it was around half of the Shadowlands launch spike. Optimistically, I don't see raid participation being more than 2/3 of Shadowlands peak raiding at the start. Unless some things change and Blizz makes some statements concerning their game/raid/content design philosophy, I could see the player participation dropping to even lower levels than Shadowlands. The current state of Dragonflight seems designed to slow the hemorrhaging of players, not to increase the player base... basically, we'll see lower participation at reduced rates of loss unless something changes.