If.
I strongly suspect that that the overwhelming majority of adventures don't break that way. Lets be clear here: I'm sure there are a fair handful of people on these forums that have some adventure or another more than once for completely difference groups. But the percentage of books sold that get used that way can be safely rounded to zero. The number of adventure books that used to run an adventure to completion even once is almost certainly a pretty small fraction of the ones that actually see a table, which is absolutely a small fraction of the ones sold. And I explicitly picked a popular and enduring one to even estimate the number as high as I did.
Yeah, I realize I could be the exception. I've run Strahd, Princes of the Apocalypse, Phandelver, and Tomb of Annhilation for multiple groups. That said, I've run others only once. And others (Avernus) not at all.
I wonder if some of us on these boards "might" purchase too many books? (Heck, I know I do.) Other DMs I know actually run the adventures they purchase - and don't buy another book until they "need" another book. (Wild idea, right?) For example, I have a friend who has purchased and run one WotC adventure (Strahd). Another picked up the Critical Role campaign and is running that for his family - and I think that is the first official module he's bought.
If we consider that most of WotC's customers (by their own metrics) are 1) new to the hobby and 2) are of the millennial or younger generation [and maybe have less discretionary income and time] - it would stand to reason that they might not purchase as much as an old-timer like me. Ergo, they likely wouldn't buy stacks of books they're not going to use.
Yes, we deserve better. But we're not going to get it. If we were, it would have already happened decades ago. The bulk of the books are sold to people who are perfectly happy to read them and never play. This is true for adventures, for PHBs, even for entire game systems. It's true among the super casuals, and it's even more true among the dedicated "most of my life revolves around the hobby" types. That's the reality of the hobby we're a part of. It only changes if people stop buying stuff they'll read but never use. And if that happened, there would suddenly be a whole lot fewer games on the market. A significant number of companies in the industry collapsing overnight as their margins buckle completely. And even then, I'm not convinced it would actually make the big dogs suddenly start investing a whole lot of time and effort into making the adventures better, they'd just try to make them more cheaply to make up for the lost numbers.
But it would make a difference to my wallet and bookshelves. And that's where it needs to start (for me).
I watched a video recently from a guy I like to watch - Uncle Atom (Adam?) from Tabletop Minions. He talks about Warhammer and other miniature wargames, but the advice is relevant to any hobby collector. I'll link the video here.
He talks about how to ignore your "goblin brain," that part of us that is driven by FOMO and a desire to complete collections (an impossible task).
For me, I'm going to take some of this advice to heart. I'm going to stop buying "the new hotness" in gaming, new adventures that I don't know when I'm going to run, etc.
While it may not ensure that companies make "better" adventures, it does help me curate a collection I'm proud of ... and that I will use.