I'm sure a lot of it is because you can't afford to pay a writer per word for PDF products...
Imagine the numbers from the other thread about number of PDF's sold....
I don't remember them all, but I'll take 150 products sold just as a 'random' number, but the math can be used with just about any of them.
I'm also going to 'assume' a selling price of $5, which is pretty common around the industry.
So that's $750, for which the distributor will take 20%, which leaves you with $600.
Add in art and stuff, and you're probably looking at between $100 and $150 for cover art and interior art. Since I've been choosing all low numbers, I'll use $100 for my math.
Down to $500. And this thing isn't edited or in layout. So let's go on the low side, and throw in $100 for that (I'm sure it CAN be much more, depending on the product).
$400.
Now, aside from posting press releases and word of mouth, you need to advertise. Inside this is also having a website up, possibly buying ad space here at EN World. Let's put a meager $50 in advertising for the whole project.
$350.
I've checked the word count on a few of the BETTER products out there, and I'm going to go on the extremely LOW side of 25,000 words.
Now we're down to 1.4 cents a word. Not horrible, but below average. Split that $350 between multiple writers, and the amount you're bringing home isn't much.
And this is doing it 'alone' and publishing your own stuff without a publishing house. It's also choosing most of the lowest costs associated with getting this product to market. This doesn't account for the software you have to purchase to MAKE the PDF if you do it alone, which can get really expensive very quickly...especially if you want it to be high quality.
Of course, you pitch to a publisher, and your margins will probably change a bit, depending on sales, and how established you are. Figure if you're starting out, you're lucky if you and your writers are going to split $200, but then again, you don't have to worry about any of the advertising and layout stuff, the publisher takes care of that...as well as advertising. Of course, if they have a highly established customer base, then maybe it might go up a little.
Just my .02