Majoru Oakheart
Adventurer
It's possible. But there's also a couple hundred pages long complete role-playing games out there for free. So, they COULD put it out completely free. They won't. They have a bottom line to maintain and someone at WOTC figured out that with the amount of art in the books, the cost for the last couple of years of R&D, the cost of the printing, the cardboard box, the dice, the maps, etc...that a 64 page book and a 32 page book for about $20 is what they can afford to do.They could have put character creation in it and retained the $20 price tag. You can buy a complete role-playing game that's a couple of hundred pages long for $20-25.
If they had to significantly increase the page count, they'd likely need more art to fill those pages so they'd have to pay more artists. They'd need more editing and someone would have to spend more time on writing, therefore increasing the cost. They'd also be including more of their precious R&D, increasing the perceived value of the books. Companies like WOTC are very concerrned about perceived value. If you price something much lower than its perceived value then the market begins to expect products of similar cost to value ratio.
It's the same reason that the movie industry is fighting so hard to make sure downloads of movies cost $15 instead of $2. They could release them at $2 and still make money and everyone would love it. But then people would lower the value of a movie to $2 in their minds. They would begin questioning why they would ever pay for a $20 DVD when they can download a movie for $2. They'd begin questioning why they would go see a movie for $15 in theaters when they can wait and download it for $2. Then the industry makes considerably less profit.
On the other hand, if they use their power to make sure everyone HAS to charge $15 for movie downloads then everyone has to make a value judgement between a $20 DVD and a $15 download.
This is a similar situation. It's possible for them to put out the entire PHB for $15. Printing likely costs less than that. They may even get the art in for that price as well. But there will be almost no profit and everyone will expect all books to be 320 pages for $15 from now on. The only way they can maintain that and likely pay their staff is to put out two or three books a month just to try to squeeze as much money out of people as possible.
On the other hand, if they release a book that costs $50 every two months, they can fulfill their goal of avoiding some of the rules bloat of previous editions while still keeping the lights on.