No, let's say the 5th edition sold 100,000 and the 4th edition sold 50,000, while Martial I, Arcane, and Primal sold 10,000 each. See? I can pull numbers out of my rear end too. And my pulled-out numbers say 5E is selling 20% better than 4E did. (Now, if you'll excuse me, I'm going to go run for political office.)How many copies of all the 3rd and 4th edition books have sold next to 5th edition? Let's say the 5th edition sold 100,000 and the 4th edition sold 50,000. Well the Martial 1 could sell 25,000 while the Arcane sells 40,000, while the primal sells 30,000.
But even assuming that more publications equals more sales, each book has a substantial overhead. You have to pay writers and editors and designers and marketers to create and advertise the thing. It has to sell enough copies of that individual book for the net revenue to cover the overhead, or it's a money-loser. There's a base number of copies you have to sell just to break even, and that number is not small.