I would say that since you stopped buying them, the adventure books have gotten better at being modular and or usable/minable for modular gaming needs (Tales from the Yawning Portal is specifically a bunch of smaller adventures, Tomb of Annihilation is a sandbox/hex-crawl island with a massive end-dungeon that can be ignored along with the overall plot if preferred, or used in isolation, Storm King's Thunder is very much more multi-outcome with more ways to go about it than the more linear railroads of the earlier ones).
That said, yes. It appears that a $50 purchase that takes up a quarter, half, or most of a 20-level campaign is the preferred model for module gaming, as far as WotC wants to be in charge of.
I will say that WotC has been upfront that it expects people to take advantage of third party products. So it might not be that WotC doesn't think that there is a market for modular style adventures, only that they don't want to attempt to make a profit doing so, given their overarching corporate strategy.
Overall, however, I've often wondered what model has been more profitable. Were B1 and B2, that you mentioned, profitable for TSR? I assume so, but I guess I don't know.