So, how do you think you make people stop buying DnD physical books AND maintain the market penetration of being able to sell them in major retailers like Wal-mart? What is the step WoTC takes?
Make their VTT super super good? That doesn't expand their reach into the general populace via sales in Wal-mart and other major Retailers. And even if you tripled the profits they made digitally... well those digital profits come from fans, and a sale to a wal-mart customer is a potential to make up to 5 to 6 new fans, which may end up buying those digital products as well, making them even more profit.
I just don't see a coherent argument for this until all brick-and-mortar stores across the country go out of business.