Of course. There is a lot more to it than that, but if you want to sum it up in a few words you want more people to buy your product than not.
You want people to buy your product, but you need to sell it at a high enough price to make a profit, and you need sell enough copies to offset production costs.
Books have two production costs. In addition to the costs of printing, which applies to each book, there is the cost of production: art, writing, editing, layout, etc. So you start out in a financial hole from writing the book, which gets deeper as you print the book, and gradually makes money as you sell copies.
The larger the print run (more copies printed at one time) the cheaper the printing cost of each book is, but the larger the initial investment. And the printing costs never reach zero. However, after a certain point, you pay off production costs and the more copies you sell, the more money you make.
Similarly, the cost of increasing the product's size goes down the larger it gets. (To a point.) The initial cost of making a book is high but adding new pages gets cheaper and cheaper. This is why it's cheaper to release one 320-page book rather than two 160-page books (plus you only pay for the cover once).
I used the earlier example of one product versus two. If you release one book to sales of 25,000 copies versus two books with sales of 15,000 copies each, the latter seems more profitable. You sold 30,000 copies. However, the print run was smaller, so less money was made on each copy. And you still need to pay off production costs. If you needed to sell 10,000 copies to turn a profit you sold 15,000 books for a profit in the former but only 10,000 at a profit: despite selling 5,000 more books you made 5,000 books' less money.
Because of this, less is more.
It is significantly better to release fewer products that appeal to more people. So it makes much, much more financial sense for WotC to, say, release one 320-page accessory that appeals to players of multiple classes than it would to release four 80-page books each focused on a single class group. The content will be cheaper for the players, the single book will sell better, the book will be more profitable for WotC, etc.
This is just the straight financials. And it does not consider the effect of diminishing the wall of books intimidating players away, or less frequent books being more anticipated, or having more time between releases allowing for more time to playtest and this increase quality.