Here's the hard truth: Wizards of the Coast doesn't expect you to buy everything. But they're also not making products just for you.
This is the catch. For the last two editions, all the D&D eggs have been in a single basket. All D&D products were really focused on a single audience: the RPG players. So the game lived or died based on how that one audience wanted to spend their money. And if that audience felt stretched thin, then sales would drop. If that one audience felt they had enough product, then sales would drop. If another game or product came out that prioritized that audience's funds, then sales would drop.
Now the D&D is being spread out. WotC is focusing on spreading out to to board gamers, video gamers, miniature war gamers, comic fans, and yes the RPG fans. So they can pull in the same revenue as monthly books but target different audiences, potentially increasing total profits.
And WotC can do so while licencing out products, keeping their own staffing and overhead costs low. Because WotC is all about maximizing profits.
This does mean fewer RPG products, but it should mean its significantly easier to afford said products as there's less cutting into the ol' wallet. And the rarer products are more exciting, since they're less common and everyday. Which might translate to higher and more sustained sales.
It's a little like going from a spoiled only child to having a couple siblings. Suddenly you have to share and not everything can be about you.
And, hopefully, with fewer books they won't need to reboot or relaunch the game after 2-4 years.
I remember seeing a lot of Board games during the 4e era but also a lot of cancelled miniature lines etc.
And then there is the other bugbear involving the DnD department not receiving the appropriate credit for products sold outside the book line. For example profits from a DnD movie, or lunchboxes or Legos need to be attributed to the DnD department.