But, that's not how business works.
Say it takes 20000 copies sold to break even on a book. I could sell 20000 copies of an infinite number of titles and never make a dime, even though my gross sales are infinite. And, in fact, that's largely what 3e and 4e looked like. You don't make 30 dollars on a 30 dollar book. WotC probably makes about 7 bucks on that book. So, 20k copies sold is 140k dollars, which, after you pay for everything, is probably close to break even.
3e and 4e, other than the core books, rarely saw sales much more than about 20-40k copies on any given book. Which meant that most of the books they were publishing were breaking even, but, not much more. In a publicly traded company with share holders, that's a problem.
5e, OTOH, has the goal of 100k copies of every single publication. And, by all accounts, they are meeting or exceeding that goal. Even with modules, which is practically unheard of since the fad years. But, the break even point for those books is still probably about 20k copies. Meaning that even though gross sales might be less in 5e, they are making far, far more profit.
It goes back to the old saw that selling two times as many copies of one book is far more profitable than regular sales of three books, even though the latter has sold 50% more books in total.