My bet is that WotC knows that they will need to price the PDFs at roughly the same price as the paper books. This is to avoid cannibalizing book sales, as well as recouping the R&D costs. People costs are much higher than material costs, and the marginal cost of a book is pretty low.
However, if they do that, that will just create a firestorm of controversy, and overall sales of books and pdfs will not be much higher than selling books alone. So they may as well just not bother.
However, if they do that, that will just create a firestorm of controversy, and overall sales of books and pdfs will not be much higher than selling books alone. So they may as well just not bother.